Building the docs locally adds lots of noise for version control

[GeigerJ2]

See below. I assume all html directories could be added to the .gitignore. The additional autogen files, as well, as they should be auto-generated when pushing anyway?

[superstar54]

There are two cases:

• the HTML files generated by autogen should be added to .gitignore.
• the HTML files generated by normal notebooks, we need to push it manually.

[GeigerJ2]

I'll make a PR!