Updated README-MAVEN.txt with required Eclipse plugins
needed to import expenses sample app as a maven project.

Review at http://gwt-code-reviews.appspot.com/1031801

Review by: drfibonacci@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9118 8db76d5a-ed1c-0410-87a9-c151d255dfc7