SLING-7167 Adjust READMEs

add uniform header linking to Sling project

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1810814 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/README.md b/README.md
index 27b7f57..8949442 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,6 @@
-Apache Sling API
+# Apache Sling API
+
+This module is part of the [Apache Sling](https://sling.apache.org) project.
 
 The Sling API defines an extension to the Servlet API 3.0 to
 provide access to content and unified access to request