readme: add tooltip for macOS users

Author: love-linger

README.md

@@ -80,6 +80,7 @@ For **macOS** users:
 * Make sure your mac trusts all software from anywhere. For more information, search `spctl --master-disable`.
 * Make sure [git-credential-manager](https://github.com/git-ecosystem/git-credential-manager/releases) is installed on your mac.
 * You may need to run `sudo xattr -cr /Applications/SourceGit.app` to make sure the software works.
+* You may need to start this app from commandline by using `open -a SourceGit` to introduce the `PATH` environment variable from your shell.
 
 For **Linux** users: