* Create discussions-graphql-api.md
Here's the PR for our manual version of the Discussions GraphQL API documentation. Per the conversation in https://github.com/github/docs-team/issues/318, the intention is to publish this guide as reference documentation until we have automation in place to generate these docs.
* style guide alignment
* rename article
* OAuth user -> OAuth app
* remove incorrect discussion description
* Use discussions product name
Co-authored-by: skedwards88 <skedwards88@github.com>