[Docs]Updates detections API (elastic#70)

* adds new rule fields

* makes things more readable??

* updates terminology where possible

* typos and stuff

* more terminology changes

* corrections and new eample

* updates-signals-endpoint

* missing comma

* corrections after reiew

* typo

* wording and typos

* updates update rule endpoint

* terminology

* corrections after review

Author: benskelker