Document the potential insecurity of --net host

Docker-DCO-1.1-Signed-off-by: Timothy <[email protected]> (github: https://github.com/timthelion)

docs/sources/reference/run.md

@@ -152,7 +152,7 @@ Supported networking modes are:
 
 * none - no networking in the container
 * bridge - (default) connect the container to the bridge via veth interfaces
-* host - use the host's network stack inside the container
+* host - use the host's network stack inside the container.  Note: This gives the container full access to local system services such as D-bus and is therefore considered insecure.
 * container - use another container's network stack
 
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