Add `brew` troubleshooting tips

Overview

I ran in to some brew problems that didn't resolve themselves until i ran brew cleanup -df. I'm not sure what other best-practices there are when running brew after it's collected some dust, but we should add some hints in case anyone else gets stuck.

Might be useful to note a good housekeeping procedure before starting the install? Something like brew update && brew cleanup -df? Could be a good addition to troubleshooting.md.

Proposal (optional)

Add a new section in troubleshooting.md that collects some brew install hints.

Possibly:

brew update && brew cleanup -df