Docs/add rust version requirement

[Aditya30ag]

Description

This PR updates the documentation to clarify the minimum supported Rust version (1.89.0) and adds instructions to update Rust using rustup update stable when an older version is installed.

Checklist

• I have run ./scripts/precommit.sh and addressed all comments

[domenukk]

I fear that we'll forget about updating the rust version in docs when we push the min version :D

[Aditya30ag]

your point is absolutely valid we can do one thing instead explicitly point one version we can ask to update the rust version if it become old

[domenukk]

We shoudl eitehr check it's the same as in
https://github.com/AFLplusplus/LibAFL/blob/4d0a5dabda6d70538a6696a1f779a34d3a656dce/crates/libafl/Cargo.toml#L15or just leave it out all together I think

[Aditya30ag]

Yes sir ,
Instead of hard-coding a Rust version in the docs we can ensure it always matches the version specified in LibAFL’s Cargo.toml, which is the real technical constraint.
or
we can also use this line - If your Rust version is too old, update it using rustup update stable.

[domenukk]

yeah just a simple info is fine. Anyd maybe link to the cargo.toml of libafl crate so it's easy to check what the current min version is

[Aditya30ag]

Is this correct

[domenukk]

older than the one listed in Cargo.toml, ...

otherwise looks good! :)

[Aditya30ag]

@domenukk sir done the all changes