docs: deduplicate CONTRIBUTING.md into docs/en/contributing.md (#8727)

* docs: deduplicate CONTRIBUTING.md into docs/en/contributing.md

Closes #8245

Merge missing bits from the root CONTRIBUTING.md into the docs version,
as suggested in the related issue:

- Add "Chat with us" section with the Mattermost link
- Mention the edge branch as the PR target and add the CREDITS.md
  first-time contributor reminder in step 4 of "Fix a bug"
- Add the "help wanted" label link alongside "good first issue"

Replace the root CONTRIBUTING.md with a short stub pointing to the
rendered Contributor Guidelines page, so Github's "New issue/PR" UI
still surfaces a link.

* Update CONTRIBUTING.md

Co-authored-by: Frans de Jonge <fransdejonge@gmail.com>

---------

Co-authored-by: Bjørn A. Andersen <polybjorn@users.noreply.github.com>
Co-authored-by: Frans de Jonge <fransdejonge@gmail.com>

CONTRIBUTING.md

@@ -1,54 +1,3 @@
 # How to contribute to FreshRSS
 
-## Chat with us
-
-Do you want to ask us some questions? Do you want to discuss with us?
-Don’t hesitate to [join our Mattermost chat](https://framateam.org/signup_user_complete/?id=e2680d3e3128b9fac8fdb3003b0024ee)!
-
-
-## Report a bug
-
-You found a bug? Don’t panic, here are some steps to report it easily:
-
-1. Search for it on [the bug tracker](https://github.com/FreshRSS/FreshRSS/issues) (don’t forget to use the search bar).
-2. If you find a similar bug, don’t hesitate to post a comment to add more importance to the related ticket.
-3. If you didn’t find it, [open a new ticket](https://github.com/FreshRSS/FreshRSS/issues/new).
-
-If you have to create a new ticket, try to apply the following advice:
-
-- Give an explicit title to the ticket so it will be easier to find it later.
-- Be as exhaustive as possible in the description: what did you do? What is the bug? What are the steps to reproduce the bug?
-- We also need some information:
-	- Your FreshRSS version (on about page or `constants.php` file)
-	- Your server configuration: type of hosting, PHP version
-	- Your storage system (SQLite, PostgreSQL, MariaDB, MySQL)
-	- If possible, the related logs (PHP logs and FreshRSS logs under `data/users/your_user/log.txt`)
-
-## Fix a bug
-
-Did you want to fix a bug? To keep a great coordination between collaborators, you will have to follow these indications:
-
-1. Be sure the bug is associated to a ticket and say you work on it.
-2. [Fork this project repository](https://help.github.com/articles/fork-a-repo/).
-3. [Create a new branch](https://help.github.com/articles/creating-and-deleting-branches-within-your-repository/). The name of the branch must be explicit and being prefixed by the related ticket id. For instance, `783-contributing-file` to fix [ticket #783](https://github.com/FreshRSS/FreshRSS/issues/783).
-4. Make your changes to your fork and [send a pull request](https://help.github.com/articles/using-pull-requests/) on the **edge branch**. Don’t forget to add your name to `CREDITS.md` if you’re contributing to FreshRSS for the very first time.
-
-If you have to write code, please follow [our coding style recommendations](https://freshrss.github.io/FreshRSS/en/developers/02_First_steps.html).
-
-> ℹ Check [`AGENTS.md`](AGENTS.md) for detailed coding conventions (both for humans and AI agents).
-
-**Tip:** if you are searching for bugs easy to fix, have a look at the « [Good first issue](https://github.com/FreshRSS/FreshRSS/issues?q=label%3A%22good+first+issue+%3Ababy%3A%22) » and/or « [Help wanted](https://github.com/FreshRSS/FreshRSS/issues?q=label%3A%22help+wanted+%3Aoctocat%3A%22) » ticket labels.
-
-## Submit an idea
-
-You have great ideas, yes! Don’t be shy and open [a new ticket](https://github.com/FreshRSS/FreshRSS/issues/new) on our bug tracker to ask if we can implement it. The greatest ideas often come from the shyest suggestions!
-
-If your idea is nice, we’ll have a look at it.
-
-## Contribute to internationalization (i18n)
-
-Learn how to contribute to translations in [the dedicated documentation](./docs/en/internationalization.md).
-
-## Contribute to documentation
-
-[The documentation](https://freshrss.github.io/FreshRSS/) always needs improvements in order to be more useful to newcomers. If you want to give some help, meet us on [the dedicated sub-folder](https://github.com/FreshRSS/FreshRSS/tree/edge/docs)!
+See the **[Contributor Guidelines](https://freshrss.github.io/FreshRSS/en/contributing.html)** for how to report or fix bugs, submit ideas, and contribute to translations, documentation, and themes.

docs/en/contributing.md

@@ -1,5 +1,10 @@
 # Contributor Guidelines
 
+## Chat with us
+
+Do you want to ask us some questions? Do you want to discuss with us?
+Don’t hesitate to [join our Mattermost chat](https://framateam.org/signup_user_complete/?id=e2680d3e3128b9fac8fdb3003b0024ee)!
+
 ## Report a bug
 
 Have you found a bug? Don’t panic, here are some steps to report it with ease:
@@ -29,13 +34,13 @@ Would you like to fix a bug? For optimum coordination between collaborators, you
 1. Be sure the bug is associated with a ticket and indicate that you’ll work on it.
 2. [Fork the project repository](https://help.github.com/articles/fork-a-repo/).
 3. [Create a new branch](https://help.github.com/articles/creating-and-deleting-branches-within-your-repository/). The name of the branch should be clear, and ideally prefixed by the related ticket id. For instance, `783-contributing-file` to fix [ticket #783](https://github.com/FreshRSS/FreshRSS/issues/783).
-4. Make your changes to your fork and [send a pull request](https://help.github.com/articles/using-pull-requests/).
+4. Make your changes to your fork and [send a pull request](https://help.github.com/articles/using-pull-requests/) on the **edge branch**. Don’t forget to add your name to `CREDITS.md` if you’re contributing to FreshRSS for the very first time.
 
 If you have to write code, please follow [our coding style recommendations](developers/02_First_steps.md).
 
 > ℹ Check [`AGENTS.md`](https://github.com/FreshRSS/FreshRSS/blob/edge/AGENTS.md) for detailed coding conventions (both for humans and AI agents).
 
-**Tip:** if you’re searching for easy-to-fix bugs, please have a look at the “[good first issue](https://github.com/FreshRSS/FreshRSS/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22)” ticket label.
+**Tip:** if you’re searching for easy-to-fix bugs, please have a look at the “[good first issue](https://github.com/FreshRSS/FreshRSS/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22)” and “[help wanted](https://github.com/FreshRSS/FreshRSS/issues?q=label%3A%22help+wanted+%3Aoctocat%3A%22)” ticket labels.
 
 ## Submit an idea