HDFS-11175. Document uppercase key names are not supported in TransparentEncryption.md. Contributed by Yiqun Lin.

(cherry picked from commit 636f7547b7067c315cf5448d77e49a8fe55651b3)
(cherry picked from commit 0df7f5cdf673d9b0f97f85099c52a0a77342836e)

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/TransparentEncryption.md

@@ -173,7 +173,7 @@ Create a new encryption zone.
 | | |
 |:---- |:---- |
 | *path* | The path of the encryption zone to create. It must be an empty directory. A trash directory is provisioned under this path.|
-| *keyName* | Name of the key to use for the encryption zone. |
+| *keyName* | Name of the key to use for the encryption zone. Uppercase key names are unsupported. |
 
 ### <a name="listZones"></a>listZones