Add installation instructions to README.md

[den1k]

#17 and #51

[qvipin]

@mhaeuser might be a good idea to add this since you are going to get an influx of users migrating from batfi to here

[mhaeuser]

Yes, it’s in the backlog (hence not closed), but I haven’t had a calm moment to write up something nice. Also the main issue is lack of Notarization, arguably it’s more important to address this… Maybe it needs an Apple Developer membership donation.