Merge pull request #703 from weaveworks/688-security-warngin

Add basic security warning.

README.md

@@ -28,8 +28,12 @@ boot2docker, replace localhost with the output of `boot2docker ip`.)
 ## <a name="requirements"></a>Requirements
 
 Scope does not need any configuration and does not require the Weave Network.
-But Scope does need to be running on every machine you want to monitor.
+Scope does need to be running on every machine you want to monitor.
 
+Scope allows anyone with access to the UI control over your containers: as
+such, the Scope app endpoint (port 4040) should not be made accessible on
+the Internet.  Additionally traffic between the app and the probe is currently
+insecure and should not traverse the internet.
 
 ## <a name="architecture"></a>Architecture