Edited Documentation for Rate functions in Custom Animations:

[sripathimanikanta]

• It was little misleading
• Added a brief note to explain how to fix it
• Added explicit code as comments in the example code

This is my first PR!!! Open for your suggestion and Advice....

Overview: What does this pull request change?

This change helps to fix this issue #4031...

Motivation and Explanation: Why and how do your changes improve the library?

This change helps in fixing documentation in Manim Building Block Page in Custom Animation Section
Where the code breaks when rate functions are used inside the played function as explained in the following example

Links to added or changed documentation pages

This is the section - https://docs.manim.community/en/stable/tutorials/building_blocks.html#creating-a-custom-animation
https://manimce--4173.org.readthedocs.build/en/4173/

Further Information and Comments

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested