CONTRIBUTING.md: Fix comments about the black formatter (#1841)

* CONTRIBUTING.md: Fix comments about the black formatter

Fixes #1840

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -37,13 +37,9 @@ We want your work to be readable by others; therefore, we encourage you to note
   - Expand acronyms because __gcd()__ is hard to understand but __greatest_common_divisor()__ is not.
   - Please follow the [Python Naming Conventions](https://pep8.org/#prescriptive-naming-conventions) so variable_names and function_names should be lower_case, CONSTANTS in UPPERCASE, ClassNames should be CamelCase, etc.
 
-
-
 - We encourage the use of Python [f-strings](https://realpython.com/python-f-strings/#f-strings-a-new-and-improved-way-to-format-strings-in-python) where the make the code easier to read.
 
-
-
-- Please consider running [__psf/black__](https://github.com/python/black) on your Python file(s) before submitting your pull request.  This is not yet a requirement but it does make your code more readable and automatically aligns it with much of [PEP 8](https://www.python.org/dev/peps/pep-0008/). There are other code formatters (autopep8, yapf) but the __black__ style is now the recommendation of the Python Core Team. To use it,
+- Please consider running [__psf/black__](https://github.com/python/black) on your Python file(s) before submitting your pull request.  This is not yet a requirement but it does make your code more readable and automatically aligns it with much of [PEP 8](https://www.python.org/dev/peps/pep-0008/). There are other code formatters (autopep8, yapf) but the __black__ formatter is now hosted by the Python Software Foundation. To use it,
 
   ```bash
   pip3 install black  # only required the first time
@@ -57,13 +53,11 @@ We want your work to be readable by others; therefore, we encourage you to note
   flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
   ```
 
-
-
 - Original code submission require docstrings or comments to describe your work.
 
 - More on docstrings and comments:
 
-  If you are using a Wikipedia article or some other source material to create your algorithm, please add the URL in a docstring or comment to help your reader.
+  If you used a Wikipedia article or some other source material to create your algorithm, please add the URL in a docstring or comment to help your reader.
 
   The following are considered to be bad and may be requested to be improved:
 
@@ -73,13 +67,12 @@ We want your work to be readable by others; therefore, we encourage you to note
 
   This is too trivial. Comments are expected to be explanatory. For comments, you can write them above, on or below a line of code, as long as you are consistent within the same piece of code.
 
-  We encourage you to put docstrings inside your functions but please pay attention to indentation of docstrings. The following is acceptable in this case:
+  We encourage you to put docstrings inside your functions but please pay attention to indentation of docstrings. The following is a good example:
 
   ```python
-  def sumab(a, b):
+  def sum_ab(a, b):
       """
-      This function returns the sum of two integers a and b
-  	  Return: a + b
+      Return the sum of two integers a and b.
       """
       return a + b
   ```
@@ -87,15 +80,14 @@ We want your work to be readable by others; therefore, we encourage you to note
 - Write tests (especially [__doctests__](https://docs.python.org/3/library/doctest.html)) to illustrate and verify your work.  We highly encourage the use of _doctests on all functions_.
 
   ```python
-  def sumab(a, b):
+  def sum_ab(a, b):
       """
-      This function returns the sum of two integers a and b
-  	  Return: a + b
-      >>> sumab(2, 2)
+      Returns the sum of two integers a and b
+      >>> sum_ab(2, 2)
       4
-      >>> sumab(-2, 3)
+      >>> sum_ab(-2, 3)
       1
-      >>> sumab(4.9, 5.1)
+      >>> sum_ab(4.9, 5.1)
       10.0
       """
       return a + b
@@ -128,12 +120,8 @@ We want your work to be readable by others; therefore, we encourage you to note
       pass
   ```
 
-
-
 - [__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.
 - If you need a third party module that is not in the file __requirements.txt__, please add it to that file as part of your submission.
 
@@ -143,17 +131,12 @@ We want your work to be readable by others; therefore, we encourage you to note
 - Strictly use snake_case (underscore_separated) in your file_name, as it will be easy to parse in future using scripts.
 - Please avoid creating new directories if at all possible. Try to fit your work into the existing directory structure.
 - If possible, follow the standard *within* the folder you are submitting to.
-
-
-
 - If you have modified/added code work, make sure the code compiles before submitting.
 - If you have modified/added documentation work, ensure your language is concise and contains no grammar errors.
 - Do not update the README.md or DIRECTORY.md file which will be periodically autogenerated by our Travis CI processes.
 - Add a corresponding explanation to [Algorithms-Explanation](https://github.com/TheAlgorithms/Algorithms-Explanation) (Optional but recommended).
 - All submissions will be tested with [__mypy__](http://www.mypy-lang.org) so we encourage to add [__Python type hints__](https://docs.python.org/3/library/typing.html) where it makes sense to do so.
 
-
-
 - Most importantly,
   - **Be consistent in the use of these guidelines when submitting.**
   - **Join** [Gitter](https://gitter.im/TheAlgorithms) **now!**