README.md

• Reproduction of renovate-issue #17963

1. Clone repository
2. Run npm install
3. Run renovate-config-validator -> error as described at issue #17963

 INFO: Validating config.js
ERROR: config.js contains errors
       "errors": [
         {
           "topic": "Configuration Error",
           "message": "Invalid `gitlabci.registryAliases.registryAliases.$CI_REGISTRY` configuration: value is not a url"
         }
       ]