Add link to docs in the About section and README

[aufdenkampe]

To easily get from the repo to the docs at https://babelizer.readthedocs.io, it would be helpful to add the url to the rendered docs to the About section under the repo Description (i.e. upper right pane of repo's landing page, editable via the gears icon).

[aufdenkampe]

The main ReadMe also has no links to the User Guide at the root of the docs, so if I navigate to https://babelizer.readthedocs.io/en/latest/readme.html I have no easy way to navigate back.

This can be quite confusing, as the README.rst and index.rst look very similar. It would be helpful to better differentiate the two and have a prominent link to the User Guide (i.e. index.rst) at the top of the ReadMe.