Update CONTRIBUTING.md

Author: trekhleb

CONTRIBUTING.md

@@ -3,3 +3,4 @@
 - As much as possible, try to follow the existing format of markdown and code.
 - Don't forget to run `npm run lint` and `npm test` before submitting pull requests.
 - Make sure that **100%** of your code is covered by tests.
+- If you're adding **new** algorithms or data structures please provide **README.md** for each of them **with explanations** of the algorithm and **with links** to further readings.