Documentation lacking about supported macOS versions

[xanarin]

I know the docs for this bridge are currently sparse, but it would be awesome if the bridge setup instructions for Mac were updated to add supported macOS versions. I attempted to migrate my bridge from normal Mac to Mac (No-SIP) over the past few days, but I spent a significant amount of time troubleshooting crashes. It turns out these crashes occurred because Barcelona does not support Catalina (10.15). The normal Mac bridge worked fine on Catalina, but once I tried to set up Barcelona I started running into issues.

I opened an (upstream?) issue on Barcelona as https://github.com/open-imcore/barcelona/issues/33 to add the supported macOS versions to that project's documentation. However, I expect that the documentation on https://docs.mau.fi is the only documentation most people will read, so I think it would be nice to document the supported macOS versions there as well.

(Also, I just wanted to add that this project is awesome and allows me to use iMessage in environments where I can't access an iPhone or Mac, so it provides a lot of value to me. Thanks for putting in the continuing effort to develop and update it!)