Create contributing.md file (#492)

* Create contributing.md file

contributing.md for ONNX

* Update contributing.md

* Update contributing.md

Author: Mstronach

contributing.md

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+Contribution Guidelines
+=======================
+
+How to be a Contributor
+---
+
+To contribute to Core ML via onnx-coreml repository, a Contributor License Agreement (CLA) must be signed. This can be found [here](https://cla-assistant.io/onnx/onnx-coreml) or will be attached as a comment when your first pull request is created.
+
+**Core ML Open Source Community**
+
+The Core ML open source community welcomes all contributions and ideas to grow the product. This can occur within this repo as well as [coremltools](https://github.com/apple/coremltools) or [tf-coreml](https://github.com/tf-coreml/tf-coreml).
+
+This could be provided in a couple of ways:
+
+* Discovering and logging a **bug**, submitting an idea for a **feature request** (or **enhancement** to an existing feature) or asking a **question** through the use of the templates: [onnx-coreml issue](https://github.com/onnx/onnx-coreml/issues/new/choose)
+
+* Submit a **pull request** for additional functionality that you have completed: [onnx-coreml PR](https://github.com/onnx/onnx-coreml/pulls)
+    
+* Resolve an existing **issue** found in any of the repositories: [onnx-coreml open issues](https://github.com/onnx/onnx-coreml/issues)
+
+Expectations of the Community
+---
+
+The contributing guidelines and code of conduct are similar to most open source communities. This includes participating in the community through developing, receiving help and answering questions as well as engaging in a highly motivate, positive environment. 
+
+Additionally, this includes but is not limited to:
+
+* Providing comments that are helpful, motivating and constructive
+* Being respectful of others within the community
+* Collaborate with others to produce new, useful contributions to the community
+
+## Github Best Practices for Core ML Community
+
+While participating in the Core ML community, to ensure that issues and pull requests are able to be addressed quickly, please ensure that the following is being done:
+
+* Checking to see if your issue already exists
+* Following pre-existing templates 
+* Promptly replying to any requests or questions posed by others within the community on your issue / PR
+
+Code of Conduct
+---
+Our goal is to house an inclusive, welcoming open source community. This includes treating all members of the community equally 
+and with respect. We as contributors and maintainers pledge to making participation in our project and our community a harassment-free 
+experience for everyone, regardless of age, body size, disability, ethnicity, sex characteristics, gender identity and expression, 
+level of experience, education, socio-economic status, nationality, personal appearance, race, religion, or sexual identity and orientation.
+
+As project maintainers, we will monitor community behaviour to ensure acceptable behaviour. If instances of abusive, harrasement or otherwise
+unacceptable behaviour ocur, please contact coreml-conduct@group.apple.com. 
+
+The Code of Conduct is adapted from the Contributor Covenant, found [here](https://www.contributor-covenant.org)
+
+## What to expect as a Contributor to Core ML
+
+### Lifecycle of Issues
+
+Once an issue has been submitted it will be triaged and appropriate labels will be added. The issue will then either be slotted in to an upcoming release, commented on for additional information or placed in the backlog for a future release. 
+
+#### Use of templates
+There will be a provided template when submitting your issue. Please ensure that this is used and filled in as much as possible to help others in the community in understanding the issue so that they are able to provide a response easily. 
+
+If applicable, please provide the model that was being used when logging the issue, so that the issue is able to be reproduced.
+
+#### Labels
+Please check the labels page under each repository for a further description of each label. These labels will be added by project maintainers depending on need. Typically an issue can be given any of the following labels:
+
+Status → What stage of the process the issue is in (turquoise) 
+
+* Triaged, awaiting response, duplicate, repro needed, investigation or needs discussion
+
+Type  → Issue is classified based on the category it belongs to (red) 
+
+* bug, clarification, docs, enhancement, feature request, perf, question
+
+Release → If the issue is scheduled to be resolved in a specific release, it will be added (yellow)
+
+Other → this may vary depending on the repository
+
+* good first issue, help wanted
+
+### Lifecycle of Pull Requests
+
+Any pull request submitted to the repositories will be reviewed by a member of the community and upon approval by a Core ML team member can be merged to the master branch. If you are new to GitHub, please find more information regarding creating pull requests here (https://help.github.com/en/articles/creating-a-pull-request).
+
+Developing in onnx-coreml
+---
+
+Additional information regarding APIs, installation and dependencies and more can be found in the readme.md file, [here](https://github.com/onnx/onnx-coreml).
+