Consider documenting the 429 error response #40

Problem description
From the API Design Guide:

Error statuses 400, 404, 409, 422, 429: These error statuses SHOULD be documented based on the API design and the functionality involved. Subprojects evaluate the relevance and necessity of including these statuses in API specifications.

Expected action
Consider if implementations of this API may be subject to spike arrest and/or quota policies. If so, consider explicitly documenting the 429 error response code as a possible error for this API.

Additional context
None