Update hsetex.md

Author: viktoriya-kutsarova

content/commands/hsetex.md

@@ -78,7 +78,8 @@ command_flags:
 - fast
 complexity: O(N) where N is the number of fields being set.
 description: Set the value of one or more fields of a given hash key, and optionally
-  set their expiration.
+  set their expiration. If key already holds a value, it is overwritten. Any previous time to live
+  associated with the key is discarded on successful HSETEX operation.
 group: hash
 hidden: false
 key_specs: