doc: "Edit on github" links are broken

[okurz]

Each documentation page shows a "Edit on GitHub" link on top-right corner, e.g. http://borgbackup.readthedocs.org/en/stable/index.html references https://github.com/borgbackup/borg/blob/55fef2457e483701254e5b2a7d4a1a60963971a8/docs/index.rst which is broken. Same as on other subpages.

[ThomasWaldmann]

This issue is tracked there:

readthedocs/readthedocs.org#1820

[anarcat]

... and was originally reported in #413.

[ThomasWaldmann]

Closing this as duplicate as it is not in our codebase and the issue is tracked in rtd issue tracker.