docs: update installation command for macOS (#270)

* Update installation command for macOS

* Apply suggestion from @caarlos0

Co-authored-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com>

---------

Co-authored-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com>

Author: diceroll123

README.md

@@ -71,7 +71,7 @@ Names are the same as the flags themselves.
   <summary>macOS</summary>
 
 ```bash
-brew install caarlos0/tap/svu
+brew install --cask caarlos0/tap/svu
 ```
 
 </details>