Include mypy instructions in CONTRIBUTING.md
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e4c81a5ecd98..76ee1312f345 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -155,6 +155,8 @@ We want your work to be readable by others; therefore, we encourage you to note
       return a + b
   ```
 
+  Instructions on how to install mypy can be found [here](https://github.com/python/mypy). Please use the command `mypy --ignore-missing-imports .` to test all files or `mypy --ignore-missing-imports path/to/file.py` to test a specific file.
+
 - [__List comprehensions and generators__](https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions) are preferred over the use of `lambda`, `map`, `filter`, `reduce` but the important thing is to demonstrate the power of Python in code that is easy to read and maintain.
 
 - Avoid importing external libraries for basic algorithms. Only use those libraries for complicated algorithms.

### **Describe your change:**



* [ ] Add an algorithm?
* [ ] Fix a bug or typo in an existing algorithm?
* [x] Documentation change?

### **Checklist:**
* [ ] I have read [CONTRIBUTING.md](https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md).
* [x] This pull request is all my own work -- I have not plagiarized.
* [x] I know that pull requests will not be merged if they fail the automated tests.
* [x] This PR only changes one algorithm file.  To ease review, please open separate PRs for separate algorithms.
* [ ] All new Python files are placed inside an existing directory.
* [ ] All filenames are in all lowercase characters with no spaces or dashes.
* [ ] All functions and variable names follow Python naming conventions.
* [ ] All function parameters and return values are annotated with Python [type hints](https://docs.python.org/3/library/typing.html).
* [ ] All functions have [doctests](https://docs.python.org/3/library/doctest.html) that pass the automated testing.
* [ ] All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
* [ ] If this pull request resolves one or more open issues then the commit message contains `Fixes: #{$ISSUE_NO}`.
