Move documentation from DokuWiki page to GitHub repo

[woolfg]

The documentation of the plugin is currently maintained at https://www.dokuwiki.org/plugin:gitbacked - As agreed with @mhoffrog, the documentation should be moved to the GitHub repo and a feature list should be added on the DokuWiki plugin page.

• Move documentation from https://www.dokuwiki.org/plugin:gitbacked into the README.md
• Create license file in repo to get rid of the license section in README.md
• Create feature list (and maybe also a better description) to promote plugin on https://www.dokuwiki.org/plugin:gitbacked

💚 Contribution welcome: if you want to take over this issue, please, drop a message 💚

[ochurlaud]

How are you going to update the dokuwiki.org/plugin page? Is there something automatic?

I don't think "normal" users should go to github to know how to use a plugin. It should stay on the wiki (or be automatically updated) on the wiki