Add meaning of 'active' in 'weave status ipam'

site/tasks/ipam/troubleshooting-ipam.md

@@ -50,7 +50,7 @@ peers and their reachability can be obtained with
 
 ```
 $ weave status ipam
-00:00:00:00:00:01(one)      349526 IPs (33.3% of total)
+00:00:00:00:00:01(one)      349526 IPs (33.3% of total) (2 active)
 00:00:00:00:00:02(two)      349525 IPs (33.3% of total)
 00:00:00:00:00:03(three)    349525 IPs (33.3% of total) - unreachable!
 ```
@@ -59,6 +59,8 @@ Columns are as follows:
 
 * Peer Name and Nickname
 * Absolute quantity/percentage of allocation range managed by peer
+* Active - number of IP addresses in use on that peer - this is only
+  available for the peer where you run the status command.
 * Indication of unreachability. This means that the peer is not
   visible (directly or indirectly) to the peer on which `weave status
   ipam` was run; whilst this could be a transient condition due to a