Add documentation for integration APIs

Editor assessment

The subject is fully self-contained: documentation for the integration APIs was added, and a reader needs no diff to know exactly what appeared and where it belongs. Docs is the accurate type, the missing scope is unimportant because the subject localizes the change, and no body is needed for a contained page addition, which the do-not-penalize guidance covers. The trailing pull-request number is the conventional squash-merge marker. Hygiene is clean: imperative shape, no trailing period, no junk, sensible length. A small, complete, publishable message.