[Documentation] Add brew.sh for macos to install flutter

[superbonaci]

Add brew.sh to install flutter in macos readme:
https://github.com/CCExtractor/ccextractorfluttergui/blob/master/INSTALL.MD

https://formulae.brew.sh/cask/flutter#default

[eshant742]

Hi @superbonaci , can you assign this issue to me? I can look into it.

[superbonaci]

I can't do that but if you submit a pull request... we could make a fork.

[eshant742]

Thanks for the suggestion I will fork the repository, work on the fix, and submit a pull request soon.