Ceph: Improve notes in values.yaml

This PS improves the notes in the conf.pool section to describe
what they do.

Change-Id: I8fb1f1053c7b47b8fe8ea41bc3bedf10d6c9dc7c

ceph/values.yaml

@@ -192,17 +192,26 @@ conf:
     rgw: true
     mgr: true
   pool:
+  #NOTE(portdirect): this drives a simple approximation of
+  # https://ceph.com/pgcalc/, the `target.osd` key should be set to match the
+  # expected number of osds in a cluster, and the `target.pg_per_osd` should be
+  # set to match the desired number of placement groups on each OSD.
     crush:
       #NOTE(portdirect): to use RBD devices with Ubuntu 16.04's 4.4.x series
       # kernel this should be set to `hammer`
       tunables: null
     target:
+      #NOTE(portdirect): arbitrarily we set the default number of expected OSD's to 5
+      # to match the number of nodes in the OSH gate.
       osd: 5
       pg_per_osd: 100
     default:
       #NOTE(portdirect): this should be 'same_host' for a single node
       # cluster to be in a healthy state
       crush_rule: replicated_rule
+    #NOTE(portdirect): this section describes the pools that will be managed by
+    # the ceph pool management job, as it tunes the pgs and crush rule, based on
+    # the above.
     spec:
       # RBD pool
       - name: rbd