DOC: management: Correct example reload command in the document

Current example is:

  `echo "reload" | socat /var/run/haproxy-master.sock`

it will cause socat error:

  `exactly 2 addresses required (there are 1); use option "-h" for help`

Correct working command is:

  `echo "reload" | socat /var/run/haproxy-master.sock stdin`
diff --git a/doc/management.txt b/doc/management.txt
index 3770c89..a1c5b4c 100644
--- a/doc/management.txt
+++ b/doc/management.txt
@@ -3296,7 +3296,7 @@
 
 Example:
 
-  $ echo "reload" | socat /var/run/haproxy-master.sock
+  $ echo "reload" | socat /var/run/haproxy-master.sock stdin
 
 Note that a reload will close the connection to the master CLI.