doc: Add a section for Github Pages incremental build

[SilverRainZ]

Purpose

I created a general tool for enabling Sphinx incremental builds in any CI/CD environment and integrated with the sphinx-notes/pages action. I hope it can be mentioned in Sphinx documentation so more people can speed up the documentation build easily.

The sphinx-notes/pages already have 1800+ users on Github, so I think it's stable enough and worth recommending.

References

• I got idea from https://github.com/sphinx-doc/sphinx/pull/11595, and I will create a section for GitLab in the future PR