Update valkey-json example (#378)

Update and mention the return value of JSON.SET.

Signed-off-by: Binbin <[email protected]>

Author: enjoy-binbin

topics/valkey-json.md

@@ -187,6 +187,7 @@ OK
 [{"price":15,"sold":false,"title":"abc"}]
 
 127.0.0.1:6379> JSON.SET k2 . '[1,2,3,4,5]'
+OK
 127.0.0.1:6379> JSON.GET k2 $.*.[?(@>2)]
 "[3,4,5]"
 127.0.0.1:6379> JSON.GET k2 '$.*.[?(@ > 2)]'