add a note on the state of mercury in maven core

git-svn-id: https://svn.apache.org/repos/asf/maven/mercury/trunk@941019 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/site/xdoc/index.xml b/src/site/xdoc/index.xml
index ab1e527..94098ea 100644
--- a/src/site/xdoc/index.xml
+++ b/src/site/xdoc/index.xml
@@ -31,6 +31,7 @@
     <section name="Maven Mercury">
 
       <p>Maven Mercury is a replacement for the Maven Artifact subsystem, and a complete replacement for the HTTP/HTTPS/DAV/DAVS portions of the existing transport.</p>
+      <p><b>Note it's not currently used in maven core</b></p>
 
       <p>
         <!-- workaround for DOXIA-227: usemap attribute is stripped (fixed in Doxia 1.1, was 1.0-beta-1) -->