HBASE-22700 (addendum): Clarify ZK session timeout doc (#1748)

The current wording gives an impression the session timeout range
on the ZK side is forced to be in the range [2 * tickTime, 20 * tickTime].

This range is configurable on the ZK service side using minSessionTimeout
and maxSessionTimeout. Clarified that.

Signed-off-by: Jan Hentschel <janh@apache.org
Signed-off-by: Andrew Purtell <apurtell@apache.org>

Author: bharathv

src/main/asciidoc/_chapters/schema_design.adoc

@@ -1142,7 +1142,11 @@ Disable Nagle’s algorithm. Delayed ACKs can add up to ~200ms to RPC round trip
 Detect regionserver failure as fast as reasonable. Set the following parameters:
 
 * In `hbase-site.xml`, set `zookeeper.session.timeout` to 30 seconds or less to bound failure detection (20-30 seconds is a good start).
-- Notice: the `sessionTimeout` of zookeeper is limited between 2 times and 20 times the `tickTime`(the basic time unit in milliseconds used by ZooKeeper.the default value is 2000ms.It is used to do heartbeats and the minimum session timeout will be twice the tickTime).
+- Note: Zookeeper clients negotiate a session timeout with the server during client init. Server enforces this timeout to be in the
+range [`minSessionTimeout`, `maxSessionTimeout`] and both these timeouts (measured in milliseconds) are configurable in Zookeeper service configuration.
+If not configured, these default to 2 * `tickTime` and 20 * `tickTime` respectively (`tickTime` is the basic time unit used by ZooKeeper,
+as measured in milliseconds. It is used to regulate heartbeats, timeouts etc.). Refer to Zookeeper documentation for additional details.
+
 * Detect and avoid unhealthy or failed HDFS DataNodes: in `hdfs-site.xml` and `hbase-site.xml`, set the following parameters:
 - `dfs.namenode.avoid.read.stale.datanode = true`
 - `dfs.namenode.avoid.write.stale.datanode = true`