Create an FAQ part with issue backing

[chrysn]

Based on the input from the last CoRE/LwM2M protocol, I suggest we add an FAQ or "teaching CoAP" section to coap.technology.

If we manage to do that in a way that the section can live in a dedicated git repository, that repository's issue tracker can be a place where questions on general CoAP topics can be moved in (eg. if they show up in LwM2M's trackers), and either closed as works-for-me with a reference to existing text or processed into an FAQ entry or additional documentation.