DOC: management: document reuse and connect counters in the CSV format

Counters for connect and reuse were added in the stats with commit
f1573848 ("MINOR: backend: count the number of connect and reuse
per server and per backend") but not documented the CSV format in
management.txt
diff --git a/doc/management.txt b/doc/management.txt
index 93bee67..ba53b04 100644
--- a/doc/management.txt
+++ b/doc/management.txt
@@ -1099,6 +1099,8 @@
  81: dcon [LF..]: requests denied by "tcp-request connection" rules
  82: dses [LF..]: requests denied by "tcp-request session" rules
  83: wrew [LFBS]: cumulative number of failed header rewriting warnings
+ 84: connect [..BS]: cumulative number of connection establishment attempts
+ 85: reuse [..BS]: cumulative number of connection reuses
 
 
 9.2) Typed output format