Add documentation URL

info.xml

@@ -10,6 +10,7 @@
   </maintainer>
   <urls>
     <url desc="Main Extension Page">https://lab.civicrm.org/extensions/mjwshared</url>
+    <url desc="Documentation">https://lab.civicrm.org/extensions/mjwshared/-/blob/master/README.md</url>
     <url desc="Support">https://mjw.pt/support/mjwshared</url>
     <url desc="Release Notes">https://lab.civicrm.org/extensions/mjwshared/-/blob/master/docs/releasenotes.md</url>
     <url desc="Licensing">http://www.gnu.org/licenses/agpl-3.0.html</url>