Fixed instructions for Bitbucket

Bitbucket instructions needed some clarification. Changes include:
* Reminding users to turn on issues for Bitbucket
* Added link to Bitbucket docs
* Providing a sample url with helpful names for resources
* Changing placeholders to use the resource names in the sample url
Merge pull request #50 from crashlytics/patch/updating-docs

Fixed instructions for Bitbucket