docs: Tidy up and build from source in system_requirements

[Warrobot10]

Moved feedback to a new line in summary and added that building from source is an option in the system requirements.

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[Warrobot10]

@cla-bot check

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The cla-bot has been summoned, and re-checked this pull request!

[maxdeviant]

Appreciate you opening this, @Warrobot10!

I think we want to word this slightly differently, so closing in favor of https://github.com/zed-industries/zed/pull/11438.

[Warrobot10]

Okay, thanks!