HDFS-10807. Doc about upgrading to a version of HDFS with snapshots may be confusing. (Contributed by Mingliang Liu)

(cherry picked from commit 6742fb6e68d349055f985eb640d845e689d75384)

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

@@ -113,7 +113,7 @@ Upgrading to a version of HDFS with snapshots
 
 The HDFS snapshot feature introduces a new reserved path name used to
 interact with snapshots: `.snapshot`. When upgrading from an
-older version of HDFS, existing paths named `.snapshot` need
+older version of HDFS which does not support snapshots, existing paths named `.snapshot` need
 to first be renamed or deleted to avoid conflicting with the reserved path.
 See the upgrade section in
 [the HDFS user guide](HdfsUserGuide.html#Upgrade_and_Rollback)