etcdmain: update help message

Add experimental-peer-skip-client-san-verification flag description to
help message. Add default values.

etcdmain/help.go

@@ -200,12 +200,14 @@ Experimental feature:
     Duration of time between cluster corruption check passes.
   --experimental-enable-v2v3 ''
     Serve v2 requests through the v3 backend under a given prefix.
-  --experimental-backend-bbolt-freelist-type
+  --experimental-backend-bbolt-freelist-type 'array'
     ExperimentalBackendFreelistType specifies the type of freelist that boltdb backend uses(array and map are supported types).
-  --experimental-enable-lease-checkpoint
+  --experimental-enable-lease-checkpoint 'false'
     ExperimentalEnableLeaseCheckpoint enables primary lessor to persist lease remainingTTL to prevent indefinite auto-renewal of long lived leases.
-  --experimental-compaction-batch-limit
+  --experimental-compaction-batch-limit 1000
     ExperimentalCompactionBatchLimit sets the maximum revisions deleted in each compaction batch.
+  --experimental-peer-skip-client-san-verification 'false'
+    Skip verification of SAN field in client certificate for peer connections.
 
 Unsafe feature:
   --force-new-cluster 'false'