Link SDK docs to Matrix client-server documentation

[niklaslong]

Currently the function docs for the Request module don't link to the corresponding endpoints in the client-server docs. Suggestions in how to better organise documentation are welcome, my current thinking is having the endpoint path as the first line (linked to the Matrix docs for that endpoint) would make it easier to navigate, e.g. server_capabilities:

A developer searching for a function to query an endpoint would be able to search by endpoint path as well. In the detailed view of a function, we could then move the description below that to give more context: