Added initial brew troubleshooting info

What does this Merge Request do?

This MR adds a small section in troubleshooting.md that adds some info about brew doctor, brew cleanup, and has links to the brew docs directly.

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.

Closes #912 (closed)