Add a section for did resolution https bindings / error code to http status code

[aljones15]

Adding error codes specific to this spec to did-resolution will lead to the did-resolution spec being filled with error codes that are unrelated to did-resolution itself. It would be better to add a section to this spec that links to the did-resolution https binding stage and then lists the errors from the spec, their respective codes, and their respective http status codes when being resolved as described in did-resolution. Alternatively, a new spec could be created describing resolving did keys, but might not be needed.