Updated CompundInterest.py and added readme.md

[Code-Builder-io]

PR Title

Compound Interest.py

Summary

summary...

Description

The changes are as follows:

• Change 1:Fixed some typos and also add f string for smoothness
• Change 2:Added a readme file

Checks

in the repository

• [x] Made no changes that degrades the functioning of the repository
• [x] Gave each commit a better title (unlike updated README.md)

in the PR

• [x] Followed the format of the pull_request_template
• [x] Made the Pull Request in a small level (for the creator's wellfare)
• [x] Tested the changes you made

Thank You,

Aryan Tiwari