Update README with missing Redis measurements (#3582)

plugins/inputs/redis/README.md

@@ -87,6 +87,8 @@ Additionally the plugin also calculates the hit/miss ratio (keyspace\_hitrate) a
 
     **Replication**
     - connected_slaves(int, number)
+    - master_link_down_since_seconds(int, number)
+    - master_link_status(string)
     - master_repl_offset(int, number)
     - repl_backlog_active(int, number)
     - repl_backlog_size(int, bytes)