Technically saying `tty.ReadStream#setRawMode()` is correct,
but since a typical use cannot instantiate `tty.ReadStream` themselves,
and 99% of the time the only instance is `process.stdin`,
then a little clarification seemed necessary.
The overall goal here is to make readline more interoperable with other node
Streams like say a net.Socket instance, in "terminal" mode.
See #2922 for all the details.
Closes #2922.
