[DRE-maint] Bug#742407: rails-4.0: Provide README.source

[Christian Hofstaedtler]

Source: rails-4.0
Version: 4.0.2+dfsg-2
Severity: normal

Dear Maintainer,

please provide a README.source which demonstrates how to package a new
upstream version.

Neither uscan nor uscan + debian/dfsg-repack.sh yield a useful new
orig.tar.gz.

Thanks,
Christian