grim/hgkeeper

Move to the docs to the readthedocs theme and work around the jinja2 bug
This documentation gets deployed to
[docs.imfreedom.org/hgkeeper](https://docs.imfreedom.org/hgkeeper/) via CI.
To build it locally it requires the
[include-markdown](https://github.com/mondeja/mkdocs-include-markdown-plugin)
plugin.