docs setup (#61)

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CONTRIBUTING.md

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+## Contributing to Ultralytics: The YOLO framework
+
+We love your input! We want to make contributing to YOLOv5 as easy and transparent as possible, whether it's:
+
+Reporting a bug
+Discussing the current state of the code
+Submitting a fix
+Proposing a new feature
+Becoming a maintainer
+
+Here are some things to keep in mind when making PRs:
+
+### Docstrings
+
+Not all functions or classes require docstrings but when they do, we follow [google-stlye docstrings format](https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings). Here is an example:
+
+```
+'''
+   What the function does - performs nms on given detection predictions
+
+    Args:
+        arg1: The description of the 1st argument
+        arg2: The description of the 2nd argument
+
+    Returns:
+        What the function returns. Empty if nothing is returned
+
+    Raises:
+        Exception Class: When and why this exception can be raised by the function.
+'''
+```