Added known problem to comparison_chain docs

[pro-grammer1]

changelog: Added documentation to comparison_chain that explains a possible performance penalty, according to issue #5354

This is my first PR, I hope everything has been done correctly.

Fixes #5354

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @ebroto (or someone else) soon.

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[ebroto]

Thanks and welcome to Clippy!

[ebroto]

@bors r+

[bors]

📌 Commit cb6a654 has been approved by ebroto

[bors]

⌛ Testing commit cb6a654 with merge e42ba48...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: ebroto
Pushing e42ba48 to master...

[JeromeSchmied]

If #5354 was resolved by this pr, shouldn't clippy docs be updated?
clippy docs still says:

Known problems

The match statement may be slower due to the compiler not inlining the call to cmp. See issue #5354