Merge branch 'robots-help' into 'master'

Add the /help page in robots.txt

Closes #44433

See merge request gitlab-org/gitlab-ce!17928

public/robots.txt

@@ -20,6 +20,7 @@ Disallow: /projects/new
 Disallow: /groups/new
 Disallow: /groups/*/edit
 Disallow: /users
+Disallow: /help
 
 # Global snippets
 User-Agent: *