Homebrew: Mention additional security options and fix broken links

[gripedthumbtacks]

Options:

HOMEBREW_NO_INSECURE_REDIRECT=1
HOMEBREW_CASK_OPTS=--require-sha
HOMEBREW_NO_ANALYTICS=1

These links are bad:

https://github.com/Homebrew/brew/blob/master/share/doc/homebrew/Installation.md

https://github.com/Homebrew/brew/blob/master/share/doc/homebrew/Analytics.md

[MatthewHerbst]

Update links are:

HOMEBREW_NO_ANALYTICS=1/brew analytics off: https://docs.brew.sh/Analytics

HOMEBREW_NO_INSECURE_REDIRECT=1: https://github.com/Homebrew/brew/blob/9bc17c8a82a36d9676528f761eaec3961f240cc8/docs/Manpage.md#L1124

HOMEBREW_CASK_OPTS=--require-sha: Homebrew/homebrew-cask#18831

[Danrancan]

How do I go about activating these rules in Homebrew?

HOMEBREW_NO_INSECURE_REDIRECT=1
HOMEBREW_CASK_OPTS=--require-sha

Are they commands or lines in some file?