Clarify requirement for Python 3.6 or later

docs/installation/3-netbox.md

@@ -1,13 +1,15 @@
 # NetBox Installation
 
-This section of the documentation discusses installing and configuring the NetBox application. Begin by installing all system packages required by NetBox and its dependencies:
+This section of the documentation discusses installing and configuring the NetBox application itself.
 
 ## Install System Packages
 
+Begin by installing all system packages required by NetBox and its dependencies. Note that beginning with NetBox v2.8, Python 3.6 or later is required.
+
 ### Ubuntu
 
 ```no-highlight
-# apt-get install -y python3 python3-pip python3-venv python3-dev build-essential libxml2-dev libxslt1-dev libffi-dev libpq-dev libssl-dev zlib1g-dev
+# apt-get install -y python3.6 python3-pip python3-venv python3-dev build-essential libxml2-dev libxslt1-dev libffi-dev libpq-dev libssl-dev zlib1g-dev
 ```
 
 ### CentOS

docs/installation/upgrading.md

@@ -4,6 +4,9 @@
 
 Prior to upgrading your NetBox instance, be sure to carefully review all [release notes](../../release-notes/) that have been published since your current version was released. Although the upgrade process typically does not involve additional work, certain releases may introduce breaking or backward-incompatible changes. These are called out in the release notes under the version in which the change went into effect.
 
+!!! note
+    Beginning with version 2.8, NetBox requires Python 3.6 or later.
+
 ## Install the Latest Code
 
 As with the initial installation, you can upgrade NetBox by either downloading the latest release package or by cloning the `master` branch of the git repository.