Add note on setting loglevel

README.md

@@ -168,6 +168,12 @@ snappy-java uses sbt (simple build tool for Scala) as a build tool. Here is a si
     > findbugs         # Produce findbugs report in target/findbugs
     > jacoco:cover     # Report the code coverage of tests to target/jacoco folder    
 
+If you need to see detailed debug messages, launch sbt with `-Dloglevel=debug` option:
+
+```
+$ ./sbt -Dloglevel=debug
+```
+
 For the details of sbt usage, see my blog post: [Building Java Projects with sbt](http://xerial.org/blog/2014/03/24/sbt/)
 
 ## Miscellaneous Notes