Fix Readthedocs

[dafnevk]

The documentation hasn't built correctly on readthedocs, so it still shows an old version of the documentation.

[lyashevska]

Read the docs build returns: ERROR: Could not open requirements file: [Errno 2] No such file or directory: 'requirements.txt'

Which is likely to be related to this: https://github.com/readthedocs/readthedocs.org/issues/3140

Addressed in #317 which is under review now.