README: sort en/disabling section, fix typos, add note

[Lotterleben]

it took me a while to figure out why cargo clippy -- -Aclippy::pedantic -Wclippy::items-after-statements still showed me all the lints. At first I thought it was due to the missing spaces in the current example and I debugged that until I stumbled across an issue noting that you have to touch a random file or run cargo clean when you're running clippy repeatedly on an unchanged codebase. This PR is an attempt to save the next person some time and also structure the "Allowing/denying lints" section a bit more while we're at it.

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Please keep the line below
changelog: none

[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.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[ebroto]

Thanks for your contribution!

FYI this happens because cargo does not know that flags passed to Clippy have changed. I think I may have a solution to this (discussed in #5214), so I hope I can revert the note you added soon :)

@bors r+

[bors]

📌 Commit 8ba18ae has been approved by ebroto

[bors]

⌛ Testing commit 8ba18ae with merge 0cba5e6...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: ebroto
Pushing 0cba5e6 to master...

[Lotterleben]

Yay! Thanks for the hint, I'll keep an eye on 5214 :)