docs: Minor clarification around globalOutstandingLimit comments

This comment better explain how someone with a typical 3-node ensemble may end up with a 500 limit by default.

The code that "causes" this is here: https://github.com/apache/zookeeper/blob/cedf09370b88b682ae4f7bcd29c683798fa31928/zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/LeaderZooKeeperServer.java#L166-L170

Author: Vitaliy <vitaliyf@users.noreply.github.com>

Reviewers: maoling <maoling@apache.org>

Closes #1946 from vitaliyf/docs-globaloutstandinglimit-comments

zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md

@@ -620,9 +620,11 @@ property, when available, is noted below.
     Clients can submit requests faster than ZooKeeper can
     process them, especially if there are a lot of clients. To
     prevent ZooKeeper from running out of memory due to queued
-    requests, ZooKeeper will throttle clients so that there is no
-    more than globalOutstandingLimit outstanding requests in the
-    system. The default limit is 1,000.
+    requests, ZooKeeper will throttle clients so that there are no
+    more than globalOutstandingLimit outstanding requests across
+    entire ensemble, equally divided. The default limit is 1,000
+    and, for example, with 3 members each of them will have
+    1000 / 2 = 500 individual limit.
 
 * *preAllocSize* :
     (Java system property: **zookeeper.preAllocSize**)
@@ -635,14 +637,14 @@ property, when available, is noted below.
 * *snapCount* :
     (Java system property: **zookeeper.snapCount**)
     ZooKeeper records its transactions using snapshots and
-    a transaction log (think write-ahead log).The number of
+    a transaction log (think write-ahead log). The number of
     transactions recorded in the transaction log before a snapshot
     can be taken (and the transaction log rolled) is determined
     by snapCount. In order to prevent all of the machines in the quorum
     from taking a snapshot at the same time, each ZooKeeper server
     will take a snapshot when the number of transactions in the transaction log
     reaches a runtime generated random value in the \[snapCount/2+1, snapCount]
-    range.The default snapCount is 100,000.
+    range. The default snapCount is 100,000.
 
 * *commitLogCount* * :
     (Java system property: **zookeeper.commitLogCount**)