Update README.md

Add small note regarding tap trust

Close #153

Author: NextFire

README.md

@@ -33,6 +33,9 @@ brew install nextfire/tap/apple-music-discord-rpc
 brew services restart apple-music-discord-rpc
 ```
 
+_You may need to approve the installation of this third-party formula, see [tap 
+trust documentation](https://docs.brew.sh/Tap-Trust)._
+
 These commands add [this tap](https://github.com/NextFire/homebrew-tap) to
 Homebrew, install the `apple-music-discord-rpc` formula (and Deno), and enable
 the launch agent, starting it immediately.