Mention the you need corepack enabled to run this repo (#9960)

#9579 also applies here, took
like an hour to get a `yarn build` to succeed because a build was very
close to working but didn't

CONTRIBUTING.md

@@ -37,6 +37,7 @@ Use `git clone` to get a local copy of the Redwood Framework. If you've already
 ```terminal
 git clone https://github.com/redwoodjs/redwood.git
 cd redwood
+corepack enable
 yarn install
 ```