added documentation link

Author: adixon

info.xml

@@ -10,6 +10,7 @@
   </maintainer>
   <urls>
     <url desc="Licensing">http://www.gnu.org/licenses/agpl-3.0.html</url>
+    <url desc="Documentation">https://github.com/adixon/ca.civicrm.contributionrecur/blob/master/README.md</url>
   </urls>
   <releaseDate>2025-08-07</releaseDate>
   <version>1.1.0</version>