Added older release notice. (#4253)

debadair · Mpdreamz · commit 6dd02c10888e · 2019-12-10T14:16:22.000+01:00
diff --git a/docs/page_header.html b/docs/page_header.html
@@ -0,0 +1,5 @@
+<p>
+  <strong>NOTE</strong>: You are looking at documentation for an older release. 
+  For the latest information, see the 
+  <a href="../current/index.html">current release documentation</a>. 
+</p>  
