Example keywords validation (#2956)

This pull request closes #2551: making sure that the keywords don't already appear in the example's title.

I also added validation that checks that they are at least two characters long, as this is enforced by the homepage when type your search.

services/github/github-license.service.js

@@ -37,7 +37,7 @@ module.exports = class GithubLicense extends LegacyService {
           message: 'MIT',
           color: 'green',
         },
-        keywords: ['GitHub', 'license'],
+        keywords: ['license'],
         documentation,
       },
     ]