Add limits.zombies config option

docs/user-guide/configuration.md

@@ -227,7 +227,8 @@ Option                                 | Description
 -------------------------------------- | --------------------------------------
 limits.transittunnels                  | Override maximum number of transit tunnels. (default: 5000)
 limits.openfiles                       | Limit number of open file descriptors (default: 0 - use system limit)
-limits.coresize                       | Maximum size of corefile in Kb (default: 0 - use system limit)
+limits.coresize                        | Maximum size of corefile in Kb (default: 0 - use system limit)
+limits.zombies                         | Minimum percentage of successfully created tunnels under which tunnel cleanup is paused (default [%]: 0.00)
 
 ### Trust options