Making 'vendorer init' command work by including Readme.md back in GEM 

Running `vendorer init` raises exception:

```
/Users/[...]/.rvm/gems/ruby-2.0.0-p247@[...]/gems/vendorer-0.1.15/lib/vendorer.rb:57:in `read': No such file or directory - /Users/[...]/.rvm/gems/ruby-2.0.0-p247@[...]/gems/vendorer-0.1.15/Readme.md (Errno::ENOENT)
	from /Users/[...]/.rvm/gems/ruby-2.0.0-p247@[...]/gems/vendorer-0.1.15/lib/vendorer.rb:57:in `init'
	from /Users/[...]/.rvm/gems/ruby-2.0.0-p247@[...]/gems/vendorer-0.1.15/bin/vendorer:36:in `<top (required)>'
```

`vendorer init` command uses Readme.md to generate sample Vendorfile. After commit 02384a439023b0a7f42994067128110b5281360f, Readme.md is no longer included in .gem package, making `vendorer init` to not work.

This pull request simply makes Readme.md to be again included in .gem.