Merge branch 'feature/contributing' into dev

CONTRIBUTING.md

+We welcome contributions to FINN.
+
+Please follow the steps below and be sure that your contribution complies with our guidelines.
+
+1. Share your proposal via <a href="https://github.com/Xilinx/finn/issues" target="_blank">Github issues</a>. If you are looking for some issues to get started with, we have a list of <a href="https://github.com/Xilinx/finn/labels/good%20first%20issue">good first issues</a> in the issue tracker. Feel free to ask questions on the <a href="https://gitter.im/xilinx-finn/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge">FINN gitter channel as well</a>.
+
+	We welcome submissions to:
+
+	1. The FINN flow like additional custom ONNX nodes, transformation and analysis passes.
+	2. Contributions to the documentation and Jupyter notebooks
+
+	To ensure clean separation of toolflow and examples, we do not keep example networks in this repo. If you want to add example networks, we ask you to make them into a separate repo and use FINN as a dependency -- we'll be happy to add it to the list of <a href="https://xilinx.github.io/finn/community">FINN community projects</a>.
+
+2. Submitting your pull request:
+
+	1. Fork this repository to your own GitHub account using the *fork* button above.
+
+	2. Clone the fork to your local computer using *git clone*. Checkout the branch you want to work on.
+
+	3. Please install <a href="https://pre-commit.com/" target="_blank">pre-commit</a> to ensure your code is formatted to our style guidelines. The hooks we use for pre-commit can be found in <a href="https://github.com/Xilinx/finn/blob/master/.pre-commit-config.yaml" target="_blank">this file</a>
+
+	4. Modify the Python source code, Jupyter notebooks and Sphinx documentation etc. as needed.
+
+	5. Use *git add*, *git commit*, *git push* to add changes to your fork.
+
+	6. If you are introducing new functionality, add at least one unit test under the `test/` folder and make sure it passes before you submit the pull request.
+
+	7. Submit a pull request by clicking the *pull request* button on your GitHub repo:
+		1. The <a href="https://github.com/Xilinx/finn" target="_blank">master branch</a> should always be treated as stable and clean. Only hot fixes are allowed to be pull-requested. The hot fix is supposed to be very important such that without this fix, a lot of things will break.
+        2. For new features, smaller bug fixes, doc updates, and many other fixes, users should pull request against the <a href="https://github.com/Xilinx/finn/tree/dev" target="_blank">development branch</a>.
+
+3. We will review your contribution and, if any additional fixes or modifications are
+necessary, may provide feedback to guide you. When accepted, your pull request will
+be merged to the repository. If you have more questions please contact us via the <a href="https://gitter.im/xilinx-finn/community" target="_blank">FINN gitter channel</a>.