 Docs: event section of entity.md (#1711)
 Docs: event section of entity.md (#1711)

* Docs: event section of entity.md

fixed error in list of events
added event schemachanged
fixed error in componentchanged example
 using evt.detail instead of evt directly
added child-attached example

* Docs: event section of entity.md /n changed example /n added id in list of detail properties

darkwing/aframe,dmarcos/aframe,mkungla/aframe,googlecreativelab/aframe,fernandojsg/aframe,weddingdj/aframe,dmarcos/aframe,aframevr/aframe,jaxmolina/ar,ngokevin/aframe,darkwing/aframe,fernandojsg/aframe,ngokevin/aframe,wizgrav/aframe,jaxmolina/ar,RSpace/aframe,RSpace/aframe,wizgrav/aframe,chenzlabs/aframe,mkungla/aframe,chenzlabs/aframe,googlecreativelab/aframe,weddingdj/aframe,aframevr/aframe