Server Pro: Adding learn pages

If you want or need access to Overleaf documentation on your instance of Overleaf Server Pro, then set OVERLEAF_PROXY_LEARN=true (SHARELATEX_PROXY_LEARN=true for versions 4.x and earlier) in toolkit/variables.env or add the environment variable to your docker-compose file. Documentation will be enabled at the /learn path.

This will proxy requests to the main Overleaf documentation site, where it is always up to date. Note that this means your local server will perform external GET requests to overleaf.com.