Create CONTRIBUTING.md

Author: AtsushiSakai

CONTRIBUTING.md

@@ -0,0 +1,23 @@
+# Contributing to Python
+
+:+1::tada: First of off, thanks very much for taking the time to contribute! :tada::+1:
+
+The following is a set of guidelines for contributing to PythonRobotics. 
+
+These are mostly guidelines, not rules. 
+
+Use your best judgment, and feel free to propose changes to this document in a pull request.
+
+# Before contributing
+
+## Taking a look at the paper.
+
+Please check this paper to understand the philosophy of this project.
+
+- [\[1808\.10703\] PythonRobotics: a Python code collection of robotics algorithms](https://arxiv.org/abs/1808.10703) ([BibTeX](https://github.com/AtsushiSakai/PythonRoboticsPaper/blob/master/python_robotics.bib))
+
+## Check your Python version.
+
+We only accept a PR for Python 3.6.x or higher.
+
+We will not accept a PR for Python 2.x.