docs(rippled-example.cfg): add P2P link compression (#4753)

P2P link compression is a feature added in 1.6.0 by #3287.

https://xrpl.org/enable-link-compression.html

If the default changes in the future - for example, as currently
proposed by #4387 - the comment will be updated at that time.

Fix #4656

cfg/rippled-example.cfg

@@ -389,6 +389,21 @@
 #
 #
 #
+# [compression]
+#
+#   true or false
+#
+#   true - enables compression
+#   false - disables compression [default].
+#
+#   The rippled server can save bandwidth by compressing its peer-to-peer communications, 
+#   at a cost of greater CPU usage. If you enable link compression, 
+#   the server automatically compresses communications with peer servers
+#   that also have link compression enabled.
+#   https://xrpl.org/enable-link-compression.html
+#
+#
+#
 # [ips]
 #
 #   List of hostnames or ips where the Ripple protocol is served.  A default