R1:f191f66f3480

Document API management of repositories and fix some issues with creating URIs via API

Summary:
Ref T10923. Primarily documents the process for creating repositories via the API.

Also fixes a couple of issues with `repositoryPHID` not being set yet when creating URIs via the API.

Test Plan:
- Followed all documented steps to create a new repository.
- Created and edited some new URIs from the web workflow, too.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10923

Differential Revision…