doc: update eol handling in readline

This commit explicitly calls out the end of line sequences
used to generate line events in the readline module.

Fixes: nodejs#4916
PR-URL: nodejs#4927
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/readline.markdown

@@ -118,8 +118,9 @@ the `input` stream receives a `^C`, respectively known as `SIGINT`.
 
 `function (line) {}`
 
-Emitted whenever the `input` stream receives a `\n`, usually received when the
-user hits enter, or return. This is a good hook to listen for user input.
+Emitted whenever the `input` stream receives an end of line (`\n`, `\r`, or
+`\r\n`), usually received when the user hits enter, or return. This is a good
+hook to listen for user input.
 
 Example of listening for `'line'`: