README: Clarify podRestartThreshold applying to the sum over containers

calcContainerRestarts sums over containers.  The new language makes
that clear, avoiding potential confusion vs. an altenative that looked
for pods where a single container had passed the configured threshold.
For example, with three containers with 50 restarts and a threshold of
100, the actual "sum over containers" logic makes that pod a candidate
for descheduling, but the "largest single container restart count"
hypothetical would not have made it a candidate.

Also shifts labelSelector into the parameter table, because when it
was added in 29ade13 (README and e2e-testcase add for
labelSelector, 2021-03-02, kubernetes-sigs#510), it landed a few lines too high.

README.md

@@ -456,9 +456,9 @@ strategies:
 
 This strategy makes sure that pods having too many restarts are removed from nodes. For example a pod with EBS/PD that
 can't get the volume/disk attached to the instance, then the pod should be re-scheduled to other nodes. Its parameters
-include `podRestartThreshold`, which is the number of restarts at which a pod should be evicted, and `includingInitContainers`,
-which determines whether init container restarts should be factored into that calculation.
-|`labelSelector`|(see [label filtering](#label-filtering))|
+include `podRestartThreshold`, which is the number of restarts (summed over all eligible containers) at which a pod
+should be evicted, and `includingInitContainers`, which determines whether init container restarts should be factored
+into that calculation.
 
 **Parameters:**
 
@@ -469,6 +469,7 @@ which determines whether init container restarts should be factored into that ca
 |`thresholdPriority`|int (see [priority filtering](#priority-filtering))|
 |`thresholdPriorityClassName`|string (see [priority filtering](#priority-filtering))|
 |`namespaces`|(see [namespace filtering](#namespace-filtering))|
+|`labelSelector`|(see [label filtering](#label-filtering))|
 |`nodeFit`|bool (see [node fit filtering](#node-fit-filtering))|
 
 **Example:**