• Add a homebrew section, which requires producing good autogenerated homebrew files
• Clean up the cygwin autogenerated files

CC: @mkoeppe @dimpase @embray

Component: documentation

Author: John Palmieri, Matthias Koeppe

Branch/Commit: 8f064f4

Reviewer: Matthias Koeppe, John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/29558