Document MEMBER_MEMBERSHIP_INFO_URL setting.

README.md

@@ -233,6 +233,13 @@ Then  make a copy of the template file (and customize it) at
 
 Good to go :-)
 
+Settings
+========
+
+List of available settings in your `settings_local.py` file.
+
+- `MEMBER_MEMBERSHIP_INFO_URL`: Url of the page that explain how to get and renew a membership to your ISP.
+
 More information
 ================