#10242 made it so that the welcome and overview page would be copied
to index.html when generating a docs version. This change landed in
develop however, and did not make it to the release-v1.37 branch.
So we need to do this step manually here, but will not have to in
the future.
GitHub Pages will serve develop/index.html if we navigate to develop/.
index.html will still be the welcome page (for now), but if we ever decide
to change that in the future, we won't need to update this redirect page
The index.html will redirect people to the latest documentation
directory (develop), and the .nojekyll file will force github
to serve index.html files on a folder path (the user would be
served synapse/develop/index.html if they navigated to
synapse/develop).