Update homebrew.py (#59646)

##### SUMMARY

It should be known that this does not install homebrew. It only uses homebrew that is already installed. It's a core requirement.

##### ISSUE TYPE
- Docs Pull Request

+label: docsite_pr

lib/ansible/modules/packaging/os/homebrew.py

@@ -27,6 +27,7 @@ author:
     - "Andrew Dunham (@andrew-d)"
 requirements:
    - "python >= 2.6"
+   - homebrew must already be installed on the target system
 short_description: Package manager for Homebrew
 description:
     - Manages Homebrew packages