[Schema Inaccuracy] `title` and `issue` in `pulls/create` should be documented as mutually exclusive and required

[xmo-odoo]

Whatever rendering tool is used on docs.github.com may not be able to handle the oneOf trick, but it should at least be documented textually:

• title and issue can't be provided together (and I expect body is only compatible with title though I did not test it)
• either must be provided
• issue should probably be documented as converting / upgrading the issue to a PR

The description of the endpoint also contains a phrase / paragraph which doesn't seem to say / mean anything:

You can create a new pull request.

It follows a useful paragraphs which explains the ACL requirements around creating new PRs, but doesn't seem to be of any use or significance.