Added note about support for Tomcat version >= 7.0.51
Added note about support for Tomcat version >= 7.0.51

I got a fix upstream for a classloder hack in the Tomcat runner.  As a
result, this hack is no longer necessary in future versions.

melezov/xsbt-web-plugin,earldouglas/xsbt-web-plugin,earldouglas/xsbt-web-plugin