add contribution documents

Author: jshin1394

.gitignore

@@ -1,3 +1,5 @@
 dist/
+myenv/
 __pycache__/
 .DS_Store
+.pytest_cache

CONTRIBUTING.md

@@ -0,0 +1,34 @@
+# How to Contribute
+
+We'd love to accept your patches and contributions to this project. There are
+just a few small guidelines you need to follow.
+
+## Contributor License Agreement
+
+Contributions to this project must be accompanied by a Contributor License
+Agreement. You (or your employer) retain the copyright to your contribution;
+this simply gives us permission to use and redistribute your contributions as
+part of the project. Head over to <https://cla.developers.google.com/> to see
+your current agreements on file or to sign a new one.
+
+You generally only need to submit a CLA once, so if you've already submitted one
+(even if it was for a different project), you probably don't need to do it
+again.
+
+## Code reviews
+
+All submissions, including submissions by project members, require review. We
+use GitHub pull requests for this purpose. Consult
+[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
+information on using pull requests.
+
+## Testing
+
+Please make sure that your PR passes all tests by running `pytest ./src/` on your
+local machine. Also, you can run only tests that are affected by your code
+changes, but you will need to select them manually.
+
+## Community Guidelines
+
+This project follows [Google's Open Source Community
+Guidelines](https://opensource.google.com/conduct/).