Adding fuma docs in collection

[officialrajdeepsingh]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created either the topic I am modifying/adding or the collection entry I am modifying/adding.

Which change are you proposing?

• Suggesting edits to an existing topic or collection
• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

---

Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)
• Content (and my changes are in index.md)

I added the fuma docs in collections/static-site-generators. Fumadocs is a robust and beautiful documentation framework featuring a complete toolchain. It is designed for flexibility, performance, and Next.js.

---

Please note: we will close your PR without comment if you do not check the boxes above and provide ALL requested information.

[ahpook]

LGTM, Thanks!