DOC: Add missing stats fields in the management doc

Added latest fields: idle_conn_cur, safe_conn_cur, used_conn_cur, need_conn_est
diff --git a/doc/management.txt b/doc/management.txt
index eef05b0..9fd7e6c 100644
--- a/doc/management.txt
+++ b/doc/management.txt
@@ -1127,6 +1127,10 @@
  92. rtime_max [..BS]: the maximum observed response time in ms (0 for TCP)
  93. ttime_max [..BS]: the maximum observed total session time in ms
  94. eint [LFBS]: cumulative number of internal errors
+ 95. idle_conn_cur [...S]: current number of unsafe idle connections
+ 96. safe_conn_cur [...S]: current number of safe idle connections
+ 97. used_conn_cur [...S]: current number of connections in use
+ 98. need_conn_est [...S]: estimated needed number of connections
 
 For all other statistics domains, the presence or the order of the fields are
 not guaranteed. In this case, the header line should always be used to parse