Document swagger for Syringe hacking docs

[olberger]

Hacking on Syringe may be facilitated by experimenting with its API through swagger.

In short, experimenting with /syringe/swagger/ can be fun (see for instance https://labs.networkreliability.engineering/syringe/swagger/) ;-)

This should be documented IMHO.

Hope this helps,

[Mierdin]

This is fine but will be heavily impacted by Syringe MP1 nre-learning/proposals#3 so I highly advise this wait until MP1 work is done