Edit README.md to reflect tmfcore_build_war's scope

This pull request edit's README.md file to reflect the scope of this repository. In fact, this repository, named `tmfcore_build_war`, has just been forked off from `tmfcore_build`. While the objective of `tmfcore_build` was to build all possible tmfcore incarnations, this new repository just builds the `.war` file suitable to be deployed on a contained such as Tomcat 7.