Revise the description of ExternalStorageReadOnly to make it clearer.

components/policy/resources/policy_templates.json

Index: components/policy/resources/policy_templates.json
diff --git a/components/policy/resources/policy_templates.json b/components/policy/resources/policy_templates.json
index 3ed6ea907975b6d9659f519b00a1aea31c2f3b58..703dd6d071ac4834eb171dc8c1ff5f6f4a6f5394 100644
--- a/components/policy/resources/policy_templates.json
+++ b/components/policy/resources/policy_templates.json
@@ -5814,11 +5814,11 @@
       'tags': [],
       'supported_on': ['chrome_os:54-'],
       'caption': '''Treat external storage devices as read-only.''',
-      'desc': '''This policy is effective only when ExternalStorageDisabled is set to false or not configured.
+      'desc': '''This policy takes effect only when ExternalStorageDisabled is set to false or not configured.

[Andrew T Wilson (Slow), 2016/11/28 12:05:18]

I would move this description (interaction of this policy with
ExternalStorageDisabled policy) to the end, since the most important part of
this documentation is explaining what this policy does itself.

Anyhow, this description is fine, but you might consider wording it something
like: "The ExternalStorageDisabled policy takes precedence over this policy - if
ExternalStorageDisabled is set to true, then all access to external storage is
disabled and as a result this policy is ignored".

[yamaguchi, 2016/11/28 12:21:32]

Done.
Thanks so much for your help!

 
       When this policy is set to true, users cannot write anything to external storage devices.
 
-      If this setting is disabled or not configured then users can create and modify files of external storage devices which are physically writable.
+      If this setting is set to false or not configured, then users can create and modify files of external storage devices which are physically writable.
 
       Dynamic refresh of this policy is supported in M56 and later.''',
       'features': {