Add documentation link to GitHub About

[AdamRJensen]

I would like to propose that the URL to the documentation be added to the about section on GitHub (see example below). This is done for Numpy, Pandas, etc. and how I think a lot of people navigate their way to the documentation.

[mwouts]

Thank you @AdamRJensen, yes that's a great idea - I've just added a link to https://mwouts.github.io/itables/ . Thank you for proposing this!