README corrections

Instructions given were missing crucial `lib/` prefix. This has been fixed in "How to test your service" (8dd2a6e).

I also would like to point out that "Running the server locally" instructions are broken.
Assuming that `lib/` needs to be specified and `bundle exec` is used, here's how it fails:

```
$ bundle exec ruby lib/github-services.rb 
lib/github-services.rb:18:in `require': no such file to load -- basecamp (LoadError)
	from lib/github-services.rb:18
```

Look like a missing dependency.

It also talks about installing `hpricot`, but if so, shouldn't it be added to `github-services.gemspec` as a dependency.