document a *should* for the location header

[toumorokoshi]

From aep-dev/aep-openapi-linter#11, @mkistler has called out that we should include a location header in the HTTP request, to adhere to RFC 9110:

Other possible rules:

There must be a 201 response (possibly covered by aep-133-response-schema)
The 201 response has a location response header (RFC 9110 Section 15.3.2)

We should add that. Also a follow-up question: should we be doing more to hotlinking to the RFCs we've adopted and attempt to adhere to in the spec?