Update FAQ to mention the new flag

cluster-autoscaler/FAQ.md

@@ -662,6 +662,7 @@ The following startup parameters are supported for cluster autoscaler:
 | `max-node-provision-time` | Maximum time CA waits for node to be provisioned | 15 minutes
 | `nodes` | sets min,max size and other configuration data for a node group in a format accepted by cloud provider. Can be used multiple times. Format: <min>:<max>:<other...> | ""
 | `node-group-auto-discovery` | One or more definition(s) of node group auto-discovery.<br>A definition is expressed `<name of discoverer>:[<key>[=<value>]]`<br>The `aws`, `gce`, and `azure` cloud providers are currently supported. AWS matches by ASG tags, e.g. `asg:tag=tagKey,anotherTagKey`<br>GCE matches by IG name prefix, and requires you to specify min and max nodes per IG, e.g. `mig:namePrefix=pfx,min=0,max=10`<br> Azure matches by tags on VMSS, e.g. `label:foo=bar`, and will auto-detect `min` and `max` tags on the VMSS to set scaling limits.<br>Can be used multiple times | ""
+| `emit-per-nodegroup-metrics` | If true, emit per node group metrics. | false
 | `estimator` | Type of resource estimator to be used in scale up | binpacking
 | `expander` | Type of node group expander to be used in scale up.  | random
 | `write-status-configmap` | Should CA write status information to a configmap  | true