commandline: Add servo device support

BUG=chromium:1033210
TEST=run_tests

Change-Id: I15999e3c03308726a102f8db378caa478b77fe40
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1963119
Commit-Queue: Alex Klein <saklein@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/cli/command.py b/cli/command.py
index 5559061..9030b53 100644
--- a/cli/command.py
+++ b/cli/command.py
@@ -149,6 +149,10 @@
                           'use brackets (e.g. [::1]).')
     if commandline.DEVICE_SCHEME_USB in schemes:
       help_strings.append('Target removable media with usb://[path].')
+    if commandline.DEVICE_SCHEME_SERVO in schemes:
+      help_strings.append('Target a servo by port or serial number with '
+                          'servo:port[:port] or servo:serial:serial-number. '
+                          'e.g. servo:port:1234 or servo:serial:C1230024192.')
     if commandline.DEVICE_SCHEME_FILE in schemes:
       help_strings.append('Target a local file with file://path.')
     parser.add_argument('device',