Document required libraries

[HertzDevil]

This is a first attempt at crystal-lang/crystal#11488 for the reference manual. It does not include Windows specifics.

There is some overlap of information with https://github.com/crystal-lang/crystal/wiki/All-required-libraries; ideally we should move that wiki article into the reference manual too.

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[HertzDevil]

I no longer have time for this, feel free to take over the PR.

libffi and PCRE2 are currently missing

[straight-shoota]

I have enhanced the lib list. It is really a lot 🙈