Install on macOS via Homebrew in README

The application is now packaged for Homebrew:
<https://github.com/Homebrew/homebrew-core/pull/25173>

Give instructions to install it from Homebrew for macOS (it's much
easier).

Thanks to @stek29 for the formula ;-)

README.md

@@ -116,10 +116,17 @@ export PATH="$JAVA_HOME/bin:$PATH"
 
 #### Mac OS
 
-Use [Homebrew] to install the packages:
+The application is available in [Homebrew]. Just install it:
 
 [Homebrew]: https://brew.sh/
 
+```bash
+brew install scrcpy
+```
+
+Instead, you may want to build it manually. Install the packages:
+
+
 ```bash
 # runtime dependencies
 brew install sdl2 ffmpeg