doc: clarify `end` vs `finish` in streams
doc: clarify `end` vs `finish` in streams

Adds a section to the transform stream docs to clarify the
difference between the `end` event and the `finish` events.
Also clarifies the wording on the `end` event.

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node