Add contributing guidelines

CONTRIBUTING.md

@@ -0,0 +1,43 @@
+# Contribute
+
+## Introduction
+
+First, thank you for considering contributing to CameraKit-iOS! It's people like you that make the open source community such a great community! 😊
+
+We welcome any type of contribution, not only code. You can help with 
+- **QA**: file bug reports, the more details you can give the better (e.g. screenshots with the console open)
+- **Marketing**: writing blog posts, howto's, printing stickers, ...
+- **Community**: presenting the project at meetups, organizing a dedicated meetup for the local community, ...
+- **Code**: take a look at the [open issues](issues). Even if you can't write code, commenting on them, showing that you care about a given issue matters. It helps us triage them.
+
+## Reporting Issues
+
+A great way to contribute to the project is to send a detailed issue when you encounter a problem. We always appreciate a well-written, thorough bug report.
+
+Check that the project issues database
+doesn't already include that problem or suggestion before submitting an issue.
+If you find a match, add a quick "+1" or "I have this problem too."
+Doing this helps prioritize the most common problems and requests.
+
+When reporting issues, please include the following:
+
+* The version of Xcode you're using
+* The device and version of iOS you're targeting
+* The full output of any stack trace or compiler error
+* A code snippet that reproduces the described behavior, if applicable
+* Any other details that would be useful in understanding the problem
+
+This information will help us review and fix your issue faster.
+
+## Submitting code
+
+Any code change should be submitted as a pull request. The description should explain what the code does and give steps to execute it.
+
+## Code review process
+
+The bigger the pull request, the longer it will take to review and merge. Try to break down large pull requests in smaller chunks that are easier to review and merge.
+It is also always helpful to have some context for your pull request. What was the purpose? Why does it matter to you?
+
+## Questions
+
+If you have any questions, create an [issue](issue) (protip: do a quick search first to see if someone else didn't ask the same question before!).