replace yarn install step with simply executing yarn

Author: DellaBitta

CONTRIBUTING.md

@@ -232,11 +232,10 @@ In order to generate the HTML documentation files locally, go to the root of thi
 
 ```
 yarn
-yarn install
 yarn docgen devsite
 ```
 
-This will generate reference docs in `docs-devsite/`. Commit and push your the generated
+This will generate reference docs in `docs-devsite/`. Commit and push the generated
 documentation changes to GitHub following the [PR submission guidelines](#submit). Your push
 to the remote repository should force any failing documentation checks to execute again.