Add contribution guidelines (#18)

* Add contribution guidelines

CONTRIBUTING.md

@@ -0,0 +1,27 @@
+# Contribution Guidelines
+
+I am happy to accept PRs on CaskDB. For short bug/typo fixes, feel free to open a PR directly. 
+
+I accept PRs related to the challenges mentioned in the different levels. Please open a separate PR for each challenge. The shorter PR is better. It is easier to review and catch bugs.
+
+For any new feature (or the level challenges) in the db, please open a GitHub issue and discuss your design/changes first.
+
+Do *NOT* club multiple things into a single PR. This adds unnecessary work for me, and it will take way longer for me to review. 
+- CaskDB is an educational project. PRs become a great learning point for someone new to navigate the codebase and add a new feature.
+- Your PRs will be a great stepping stone for someone else who is new.
+
+Thank you!
+
+## Branches
+
+- `start-here` contains all the base challenges and test cases
+- `master` implements the base challenges
+- `final` implements challenges from different levels
+
+If your PR is a bug/typo fix, open a PR with `master` as the base. I will backport the changes to `start-here` and `final` once merged.
+
+If you are implementing something new, open a PR with `final` as the base.
+
+## "I am new; how do I get started?"
+
+Pick any challenge from any level and open a GitHub issue to discuss. I am happy to provide more resources/research papers to understand a particular concept.

README.md

@@ -123,5 +123,8 @@ $ tokei -f format.py disk_store.py
 ===============================================================================
 ```
 
+## Contributing
+All contributions are welcome. Please check [CONTRIBUTING.md](CONTRIBUTING.md) for more details.
+
 ## License
 The MIT license. Please check `LICENSE` for more details.