mark command as experimental in docs and cli

Signed-off-by: Riyaz Faizullabhoy <riyaz.faizullabhoy@docker.com>

docs/reference/commandline/trust_revoke.md

@@ -29,6 +29,8 @@ Options:
 
 `docker trust revoke` removes signatures from tags in signed repositories.
 
+`docker trust revoke` is currently experimental.
+
 ## Examples
 
 ### Revoke signatures from a signed tag

docs/reference/commandline/trust_sign.md

@@ -26,6 +26,8 @@ Sign an image
 
 `docker trust sign` adds signatures to tags to create signed repositories.
 
+`docker trust sign` is currently experimental.
+
 ## Examples
 
 ### Sign a tag as a repo admin

docs/reference/commandline/trust_view.md

@@ -30,6 +30,8 @@ new tags.
 
 By default, `docker trust view` renders results in a table.
 
+`docker trust view` is currently experimental.
+
 
 ## Examples