Add a remark about homebrew installation

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)

README.md

@@ -123,7 +123,7 @@ If you don't have maven installed, you may directly use the included [maven wrap
 
 ### [1.4 - Homebrew](#table-of-contents)
 
-To install, run `brew install openapi-generator`
+To install, run `brew install openapi-generator` (the new brew formula is pending https://github.com/Homebrew/homebrew-core/pull/28584)
 
 Here is an example usage to generate a Ruby client:
 ```sh