Missing settings in the RS documentation

[lebaudantoine]

Bug Report

Problematic behavior
Some required settings are missing to integrate the resource server backend.

Expected behavior/code

these settings:

self._client_id = settings.OIDC_RS_CLIENT_ID
self._client_secret = settings.OIDC_RS_CLIENT_SECRET

should be described in the documentation here.

[lebaudantoine]

Same for OIDC_OP_URL