Add Homebrew as installation method on MacOS

[Backroom8816]

Hi Ulyssa!

Last week iamb was added to Hombrew's repository and now mac users can install it using $ brew install iamb 1.

It seems that the brew formula is up to date with upstream and it would be nice to include this information on the install.md. I've tried to do so myself via PR but I can't fork the repo, hence opening this issue.

Thank you for your creating this amazing client 😊

[Backroom8816]

Finally I've been able to fork the repot and submitted a PR on ulyssa/iamb#303