CSHARP-578: added contributing doc.

Author: craiggwilson

CONTRIBUTING.md

@@ -0,0 +1,11 @@
+## Contributing to the driver
+
+### Bugfixes
+
+- Before starting to write code, look for existing [tickets](https://jira.mongodb.org/browse/CSHARP#selectedTab=com.atlassian.jira.plugin.system.project%3Asummary-panel) or create one for your specific issue. That way you avoid working on something that might not be of interest or that has been addressed already in a different branch.
+- Fork the [repo](https://github.com/mongodb/mongo-csharp-driver).
+- Ensure your core.autocrlf settings are set to true. [see here](http://www.mongodb.org/display/DOCS/CSharp+Driver+Tutorial#CSharpDriverTutorial-Downloading)
+- Follow the general coding style of the rest of the project.
+- Write tests and make sure they pass. [see here](http://www.mongodb.org/display/DOCS/CSharp+Driver+Tutorial#CSharpDriverTutorial-Runningunittests)
+- Your final commit should have the JIRA issue number as the first part of the commit message. [see here](https://github.com/mongodb/mongo-csharp-driver/commit/40e69fe1cf45b0ed9d68a551b0222a140fa26ba2)
+- Submit a pull request from github.