Fixed instructions for Bitbucket

Bitbucket instructions needed some clarification. Changes include:
* Reminding users to turn on issues for Bitbucket
* Providing a sample url with helpful names for resources
* Changing placeholders to use the resource names in the sample url

The changes look like this:
![screen shot 2014-07-29 at 11 15 03 am](https://cloud.githubusercontent.com/assets/1487867/3754945/2449fe5c-1820-11e4-9f09-eb26465b1af0.png)