ZOOKEEPER-4393: [ADDENDUM] Add docs of fips-mode to ZooKeeper Admin Guide (#2015)

* ZOOKEEPER-4393: [ADDENDUM] Add docs of fips-mode to ZooKeeper Admin Guide

* ZOOKEEPER-4393: Some cosmetics

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

@@ -1834,6 +1834,14 @@ and [SASL authentication for ZooKeeper](https://cwiki.apache.org/confluence/disp
 
     This parameter has no effect, unless you enable the MultiAddress feature by setting *multiAddress.enabled=true*.
 
+* *fips-mode* :
+    (Java system property: **zookeeper.fips-mode**)
+    **New in 3.8.2:**
+    Enable FIPS compatibility mode in ZooKeeper. If enabled, the custom trust manager (`ZKTrustManager`) that is used for 
+    hostname verification will be disabled in order to comply with FIPS requirements. As a consequence, hostname verification is not
+    available in the Quorum protocol, but still can be set in client-server communication. Default: **true** (3.9.0+), 
+    **false** (3.8.x)
+
 <a name="Experimental+Options%2FFeatures"></a>
 
 #### Experimental Options/Features