Adding local environment setup and pull request sections to 'CONTRIBUTING.md'.  Related to #60
Add install info for Windows users
Updating with changes based upon PR discussion:
* Using own MongoDB instance is optional
* SSH clone URL for old client compatibility
* Omit '-d' from 'npm install' of dependencies
* Improving Ruby install section and added Mac
MongoDB phrasing tweak
Merge pull request #167 from supahgreg/issue-60

Adding local env setup and pull request sections to 'CONTRIBUTING.md'