Please write documentation for using Monica's OAuth2 implementation

[phrohdoh]

There are many different ways to implement OAuth2 clients but the API settings page on Monica only shows a Client ID (which is no doubt a database PK which isn't useful to clients), a Name (is this the client_id in OAuth2 terminology?) and a Secret which I assume to be the client_secret but cannot know for sure.

As it stands I do not know what I need to do to build an integration with Monica, though I would very much like to.