Update contribution guide.

Author: trekhleb

CONTRIBUTING.md

@@ -1,6 +1,25 @@
 ## Contributing
 
+**General Rules**
+
 - 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.
+
+**Contributing New Translation**
+
+- Create new `README.xx-XX.md` file with translation alongside with 
+main `README.md` file where `xx-XX` is locale and country/region codes.
+For example `en-US`, `zh-CN`, `zh-TW`, `ko-KR` etc.
+- You may also translate all other sub-folders by creating 
+related `README.xx-XX.md` files in each of them.
+
+**Contributing New Algorithms**
+
+- Make you pull requests to be **specific** and **focused**. Instead of 
+contributing "several sorting algorithms" all at once contribute them all 
+one by one separately (i.e. one pull request for "Quick Sort", another one
+for "Heap Sort" and so on).
+- Provide **README.md** for each of the algorithms **with explanations** of
+the algorithm and **with links** to further readings.
+- Describe what you do in code using **comments**.