Change comments for improved consistency (TheAlgorithms#5223)

* Change comments for improved consistency

https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md#L56
https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md#L80
https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md#L87

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: NumberPiOso

CONTRIBUTING.md

@@ -53,7 +53,7 @@ Algorithms in this repo should not be how-to examples for existing Python packag
 Use [pre-commit](https://pre-commit.com/#installation) to automatically format your code to match our coding style:
 
 ```bash
-python3 -m pip install pre-commit  # required only once
+python3 -m pip install pre-commit  # only required the first time
 pre-commit install
 ```
 That's it! The plugin will run every time you commit any changes. If there are any errors found during the run, fix them and commit those changes. You can even run the plugin manually on all files:

DIRECTORY.md

@@ -274,6 +274,7 @@
     * [Test Send File](https://github.com/TheAlgorithms/Python/blob/master/file_transfer/tests/test_send_file.py)
 
 ## Fractals
+  * [Julia Sets](https://github.com/TheAlgorithms/Python/blob/master/fractals/julia_sets.py)
   * [Koch Snowflake](https://github.com/TheAlgorithms/Python/blob/master/fractals/koch_snowflake.py)
   * [Mandelbrot](https://github.com/TheAlgorithms/Python/blob/master/fractals/mandelbrot.py)
   * [Sierpinski Triangle](https://github.com/TheAlgorithms/Python/blob/master/fractals/sierpinski_triangle.py)
@@ -424,10 +425,12 @@
   * [Binomial Distribution](https://github.com/TheAlgorithms/Python/blob/master/maths/binomial_distribution.py)
   * [Bisection](https://github.com/TheAlgorithms/Python/blob/master/maths/bisection.py)
   * [Ceil](https://github.com/TheAlgorithms/Python/blob/master/maths/ceil.py)
+  * [Check Polygon](https://github.com/TheAlgorithms/Python/blob/master/maths/check_polygon.py)
   * [Chudnovsky Algorithm](https://github.com/TheAlgorithms/Python/blob/master/maths/chudnovsky_algorithm.py)
   * [Collatz Sequence](https://github.com/TheAlgorithms/Python/blob/master/maths/collatz_sequence.py)
   * [Combinations](https://github.com/TheAlgorithms/Python/blob/master/maths/combinations.py)
   * [Decimal Isolate](https://github.com/TheAlgorithms/Python/blob/master/maths/decimal_isolate.py)
+  * [Double Factorial Iterative](https://github.com/TheAlgorithms/Python/blob/master/maths/double_factorial_iterative.py)
   * [Double Factorial Recursive](https://github.com/TheAlgorithms/Python/blob/master/maths/double_factorial_recursive.py)
   * [Entropy](https://github.com/TheAlgorithms/Python/blob/master/maths/entropy.py)
   * [Euclidean Distance](https://github.com/TheAlgorithms/Python/blob/master/maths/euclidean_distance.py)
@@ -511,6 +514,7 @@
   * [Sum Of Arithmetic Series](https://github.com/TheAlgorithms/Python/blob/master/maths/sum_of_arithmetic_series.py)
   * [Sum Of Digits](https://github.com/TheAlgorithms/Python/blob/master/maths/sum_of_digits.py)
   * [Sum Of Geometric Progression](https://github.com/TheAlgorithms/Python/blob/master/maths/sum_of_geometric_progression.py)
+  * [Sylvester Sequence](https://github.com/TheAlgorithms/Python/blob/master/maths/sylvester_sequence.py)
   * [Test Prime Check](https://github.com/TheAlgorithms/Python/blob/master/maths/test_prime_check.py)
   * [Trapezoidal Rule](https://github.com/TheAlgorithms/Python/blob/master/maths/trapezoidal_rule.py)
   * [Triplet Sum](https://github.com/TheAlgorithms/Python/blob/master/maths/triplet_sum.py)
@@ -928,7 +932,6 @@
   * [Reverse Letters](https://github.com/TheAlgorithms/Python/blob/master/strings/reverse_letters.py)
   * [Reverse Words](https://github.com/TheAlgorithms/Python/blob/master/strings/reverse_words.py)
   * [Split](https://github.com/TheAlgorithms/Python/blob/master/strings/split.py)
-  * [Swap Case](https://github.com/TheAlgorithms/Python/blob/master/strings/swap_case.py)
   * [Upper](https://github.com/TheAlgorithms/Python/blob/master/strings/upper.py)
   * [Word Occurrence](https://github.com/TheAlgorithms/Python/blob/master/strings/word_occurrence.py)
   * [Word Patterns](https://github.com/TheAlgorithms/Python/blob/master/strings/word_patterns.py)