Update README.md

fix highlighting of code block
Merge pull request #1 from ddimmich/patch-1

Update README.md
Fixes to plugin.xml tested on cordova 2.8

* Be consistent with com.phonegap.plugin not com.phonegap.plugins
Match widgets, not just cordova in xml path
Add section to modify config.xml
Add description and engines tags
Fix README

Codeblocks need a clear newline before they start