Update stale BlobStore docs

This PR is to clean up the BlobStore Start Guide with current information and fix some minor typos.

jekyll was run locally to verify these changes.
[minor] remove the space between "provider-" and "specific? Comes out like this:

![image](https://cloud.githubusercontent.com/assets/223702/3236062/91ce90dc-f0d9-11e3-8de8-5311ad383282.png)