This very simple add-on that will create a buildinfo.txt in your dist dir that looks similar to the following:
[App Name] configuration=test built_by=davidmcnamara build_date=Thu Feb 12 2015 17:05:17 GMT+0000 (GMT) build_dir=/Users/davidmcnamara/workspace/client-hg build_host=dmcnamara-imac.local branch=default revision=hg:185:365c0862bdc5 tag=2015-w07-rc1