Create CONTRIBUTING.md

On popular demand!

Author: Karan Goel

CONTRIBUTING.md

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+How to Contribute
+==================
+
+## Solutions
+
+Please **do not send pull requests for replacing my code**. If you'd like to contribute solutions, please see the following instructions:
+
+* Solve the problem, and keep it in your repo. DO NOT send merge request yet.
+* Find the problem in this [README](https://github.com/thekarangoel/Projects/blob/master/README.md) file.
+* Edit the file in this format (notice the double square brackets):
+
+    **This is a problem** - And here goes it's description. \[[octocat]]\(link-to-octocats-solution) \[[you]]\(link-to-your-solution)
+    
+This results in something like this:
+
+**This is a problem** - And here goes it's description. [[octocat]](link-to-octocats-solution) [[you]](link-to-your-solution)
+
+* Please respect other people and do not delete or move anyone else's link. Place your solution at the end of the list of solutions.
+* Save/Commit the README.md file.
+* Send a pull request for this commit ONLY!
+
+=====================================
+
+## Problems
+
+If you have suggestions for adding or removing problems, feel free to [open an issue](https://github.com/thekarangoel/Projects/issues/new) to discuss it, or directly create a pull request after you edit the *README.md* file with necessary changes. If you add a problem, make sure you add it in the correct category.
+
+It is required that any changes made to the problems (this does not include adding solutions) in *README.md*, must be reflected in *README-scratch.md* and in *README.md* file in the relevant category folder. If you skip this step, I will not merge the changes!