Update required permissions listed in README.rst

Removed unused permissions, and changed names to those currently used by GitHub.

- code: renamed to contents as used by GitHub
- commit statuses: removed because not used by github-backup
- pages: removed because not used by github-backup
- repository hooks: renamed to webhooks as used by GitHub

README.rst

@@ -167,7 +167,7 @@ Customise the permissions for your use case, but for a personal account full bac
 
 **User permissions**: Read access to followers, starring, and watching.
 
-**Repository permissions**: Read access to code, commit statuses, issues, metadata, pages, pull requests, and repository hooks.
+**Repository permissions**: Read access to contents, issues, metadata, pull requests, and webhooks.
 
 
 Prefer SSH