Add docs for plugin API endpoints

docs/plugins/development.md

@@ -194,3 +194,50 @@ urlpatterns = [
 ```
 
 This makes our view accessible at the URL `/plugins/animal-sounds/random-sound/`. (Remember, our `AnimalSoundsConfig` class sets our plugin's base URL to `animal-sounds`.) Viewing this URL should show the base NetBox template with our custom content inside it.
+
+## REST API Endpoints
+
+Plugins can declare custom endpoints on NetBox's REST API. These behave very similarly to views, except that instead of rendering arbitrary content using a template, data is returned in JSON format using a serializer. NetBox uses the [Django REST Framework](https://www.django-rest-framework.org/), which makes writing API serializers and views very simple.
+
+First, we'll create a serializer for our `Animal` model, in `api/serializers.py`:
+
+```python
+from rest_framework.serializers import ModelSerializer
+from netbox_animal_sounds.models import Animal
+
+class AnimalSerializer(ModelSerializer):
+
+    class Meta:
+        model = Animal
+        fields = ('id', 'name', 'sound')
+```
+
+Next, we'll create a generic API viewset that allows basic CRUD (create, read, update, and delete) operations for Animal instances. This is defined in `api/views.py`:
+
+```python
+from rest_framework.viewsets import ModelViewSet
+from netbox_animal_sounds.models import Animal
+from .serializers import AnimalSerializer
+
+class AnimalViewSet(ModelViewSet):
+    queryset = Animal.objects.all()
+    serializer_class = AnimalSerializer
+```
+
+Finally, we'll register a URL for our endpoint in `api/urls.py`. This file **must** define a variable named `urlpatterns`.
+
+```python
+from rest_framework import routers
+from .views import AnimalViewSet
+
+router = routers.DefaultRouter()
+router.register('animals', AnimalViewSet)
+urlpatterns = router.urls
+```
+
+With these three components in place, we can request `/api/plugins/animal-sounds/animals/` to retrieve a list of all Animal objects defined.
+
+![NetBox REST API plugin endpoint](../media/plugins/plugin_rest_api_endpoint.png)
+
+!!! note
+    This example is provided as a minimal reference implementation only. It does not address authentication, performance, or myriad other concerns that plugin authors should have.