Links from "Source" links fail by still pointing to old docs URL/branch

[JoKeyser]

Dear PsychoPy team,

first thank you for writing such nice docs. I'm new and really need them for my onboarding :).
While reading, I noticed that the "Source" links that should link into the source files doesn't work: When clicking on them, you get a warning "404 - page not found":

For example, the link called "Source" at the bottom of https://psychopy.org/ still links to https://github.com/psychopy/psychopy/blob/master/docs/source/index.rst when I think it should link instead to https://github.com/psychopy/psychopy-docs/blob/release/source/index.rst.

<div id="sourcelink">
  <a href="[https://github.com/psychopy/psychopy/blob/master/docs/source/index.rst](view-source:https://github.com/psychopy/psychopy/blob/master/docs/source/index.rst)"
     rel="nofollow">Source</a>
</div>

I haven't yet figured out how Sphinx generates those URLs, but it would be nice if they get adapted to the new docs location (and branch name).