Standardize README landing page

Author: MariusStorhaug

README.md

@@ -6,6 +6,10 @@ GraphQL is intended to be a PowerShell module for simplifying work with GraphQL
 
 This repository is currently a placeholder. The module source still contains scaffold code, so there are no supported commands or usage examples to document yet.
 
+## Documentation
+
+When this module is implemented, command details should live in PowerShell help and generated documentation rather than being duplicated in this README.
+
 ## Contributing
 
 Issues and pull requests are welcome when implementation work begins.