improve project basic documentation

[ssbarnea]

I am raising a bug regarding the lack of useful information in the main README file

• License (also needs to be added to the repo)
• if it needs privilege escalation (install time or when
• does it needs disabling SIP (system integrity protection)
• compatibility - no High Sierra mentions, no minimal version mentions
• relatively recent build link
• CLI install method: brew (cask) install instructions
• status compatibility with VPNs as they would affect how DNS resolution works
• similar projects section - really useful, maybe even some pros/cons mentioned, could help a lot. Example: Hosts.prefpane - abandoned, last change >5 years ago.

Maybe these would look as obvious information for the author, but for someone visiting the project the first time they are not and they are key in deciding if you want to try it or.

[OJFord]

And a screenshot! Or a longer description than:

Gas Mask is simple hosts file manager for Mac OS X. It allows editing of host files and switching between them.

Reading that I have no idea how it does that, though I read elsewhere that it's menu bar based.

[2ndalpha]

If someone is willing to help on this, I'm happy to merge the PR