Add description for "--cpu-shares=0".
@@ -800,7 +800,8 @@ can be modified by changing the container's CPU share weighting relative
to the weighting of all other running containers.
To modify the proportion from the default of 1024, use the `-c` or `--cpu-shares`
-flag to set the weighting to 2 or higher.
+flag to set the weighting to 2 or higher. If 0 is set, the system will ignore the
+value and use the default of 1024.
The proportion will only apply when CPU-intensive processes are running.
When tasks in one container are idle, other containers can use the
