Custom REST endpoints (documentation)

[JeffreyArts]

The documentation for creating custom (collection) API endpoints is pretty straight forward, except for leaving out 2 essential comments.

1. When you create a new custom endpoint, it won't be accessible right away. You'll need to restart the server in order to access it. The documentation leaves this out, would be of value to add this essential detail to the documentation.
2. Custom (collection) endpoints don't show up on the API page in the admin. It is desirable to have this on this page, but until it does, it seems valuable to update the documentation that it won't show up. So people won't use it for debugging if their custom end-point is working or not.