CBG-4404: [3.2.3 backport] update rev cache size api docs for size stat (#7260)

Author: gregns1

docs/api/components/schemas.yaml

@@ -1304,7 +1304,10 @@ Database:
           type: object
           properties:
             size:
-              description: The maximum number of revisions that can be stored in the revision cache.
+              description: |-
+                The maximum number of revisions that can be stored in the revision cache.
+                Note when running with greater than 1 shard count we add 10% capacity overall to avoid early eviction when some shards fill up before others, so
+                you may find that the capacity stat (revision_cache_num_items) will climb to the defined rev cache size + 10%.
               type: string
               default: 5000
             max_memory_count_mb: