Consider supporting readthedocs

Currently, we use the free Community plan of readthedocs.com

readthedocs is becoming an important cornerstone of our documentation since we've already published libzim, libkiwix, zim-tools and python-scraperlib documentation there, and we plan to add more. I think we could / should even publish all scrapers documentation there rather than using the crappy Github wiki.

The free Community plan is mostly sufficient except that Ads are displayed throughout our documentation, see e.g. https://python-scraperlib.readthedocs.io/en/latest/

For 5$ per month, we could remove these adds and give support to readthedocs.

See https://about.readthedocs.com/pricing/#/community

Given the moderate monthly price plus the fact that it is important that we also give back to teams we like, I think that we should move to this plan.

WDYT?