README: point to Homebrew/brew README.

Point out the sections that are there so people know to go look there.

README.md

@@ -5,21 +5,14 @@ Core formulae for the Homebrew package manager.
 Just `brew install <formula>`. This is the default tap for Homebrew and is installed by default.
 
 ## Troubleshooting
-First, please run `brew update` (twice) and `brew doctor`.
+First, please run `brew update` and `brew doctor`.
 
 Second, read the [Troubleshooting Checklist](https://docs.brew.sh/Troubleshooting.html).
 
-**If you don’t read these it will take us far longer to help you with your problem.**
+**If you don't read these it will take us far longer to help you with your problem.**
 
-## Contributing
-Read [CONTRIBUTING.md](/CONTRIBUTING.md).
-
-Creating new formulae, updating existing ones, and fixing build issues is easier than you think!
-
-Try `brew edit $FORMULA` and see how you fare.
-
-## Documentation
-`brew help`, `man brew`, [Homebrew/brew's README](https://github.com/Homebrew/brew#homebrew) or check [Homebrew's documentation](https://github.com/Homebrew/brew/tree/master/docs#readme).
+## More Documentation, Contributing, Security, Community, Donations and Sponsors
+See these sections in [Homebrew/brew's README](https://github.com/Homebrew/brew#homebrew).
 
 ## Who Are You?
 Homebrew/homebrew-core's lead maintainer is [ilovezfs](https://github.com/ilovezfs).