Add a note about using the script module with pseudo-tty's lack of stderr channel (#4000)

Addresses #3610

lib/ansible/modules/commands/script.py

@@ -46,6 +46,7 @@ options:
     version_added: "1.5"
 notes:
   - It is usually preferable to write Ansible modules than pushing scripts. Convert your script to an Ansible module for bonus points!
+  - The ssh connection plugin will force psuedo-tty allocation via -tt when scripts are executed. psuedo-ttys do not have a stderr channel and all stderr is sent to stdout. If you depend on separated stdout and stderr result keys, please switch to a copy+command set of tasks instead of using script.
 author: 
     - Ansible Core Team
     - Michael DeHaan