SLING-7167 Adjust READMEs

add missing README

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1810774 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/base/README.md b/base/README.md
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+# Apache Sling Performance Test Utilities
+
+This module is part of the [Apache Sling](https://sling.apache.org) project.