add instructions to install the extension on Safari

[Tofull]

Here is the path to do it :

• read this : https://bartsolutions.github.io/2020/11/20/safari-extension/

• read this : https://developer.apple.com/documentation/safariservices/safari_web_extensions/converting_a_web_extension_for_safari

• then, use Xcode to setup the extension and follow the instructions from the doc above:

export PATH="/Applications/Xcode.app/Contents/Developer/usr/bin:$PATH"
Replace "/Applications/Xcode.app" with the path to Xcode on your system if it is installed in a different location.