list state ready for filtering in stack_ps.md

Signed-off-by: SimonHeimberg <simon.heimberg@heimberg-ea.ch>
(cherry picked from commit 6a20e87ae8e32287523bd5aa75ec63d670762ea5)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 4840a8dfbe36ad778d5a186ef670eb9e125888a2)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Upstream-commit: 9c9ff4369d36519a930803eac61d97f44ab03b09
Component: cli

Author: SimonHeimberg

components/cli/docs/reference/commandline/stack_ps.md

@@ -103,7 +103,7 @@ tz6j82jnwrx7        voting_db.1           postgres:9.4
 
 #### desired-state
 
-The `desired-state` filter can take the values `running`, `shutdown`, or `accepted`.
+The `desired-state` filter can take the values `running`, `shutdown`, `ready` or `accepted`.
 
 ```bash
 $ docker stack ps -f "desired-state=running" voting