Update README.md to reflect that commons logging is no longer required, and SLF4J may be used

Author: davidmc24

README.md

@@ -45,9 +45,9 @@ Non-Maven users should download the latest version and add it to the project's c
 
 + <a href="http://commons.apache.org/io/">Apache Commons IO 2.4</a>
 + <a href="http://commons.apache.org/lang/">Apache Commons Lang 3.1</a>
-+ <a href="http://commons.apache.org/logging/">Apache Commons Logging 1.1.1</a>
 + <a href="http://www.mozilla.org/rhino/">Rhino: JavaScript for Java 1.7R4</a>
 
+If [SLF4J](http://www.slf4j.org/) is present in the classpath, it will be used for logging.
 
 Compatibility
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