Document verb_acl middleware in default configuration

Author: fvennetier

conf/default.cfg

@@ -258,4 +258,7 @@ object_post_as_copy = false
 
 [filter:verb_acl]
 use = egg:oioswift#verb_acl
-verb_acl = PUT:127.0.0.1,127.0.0.2;DELETE:127.0.0.3,127.0.0.4;PUT,DELETE:127.0.0.4,127.0.0.6
+# White list of IP addresses prefixes. For each listed HTTP verb,
+# only allow requests coming from a client whose address matches
+# one of the prefixes.
+verb_acl = PUT:127.0.0.1,127.0.0.2,192.;DELETE:127.0.0.3,127.0.0.4;PUT,DELETE:127.0.0.4,127.0.0.6