Fix typo: Changed PostgreSQL to MySQL in README + minor improvements - #1

Description

Fixed a typo in the spring-mysql-redis/README.md file — changed “PostgreSQL” to “MySQL” in the container setup section, and improved formatting for better readability.

This contribution is part of Keploy Fellowship Task 2 – Open Source Contribution.

Type of change

• Documentation update (README improvement)

How Has This Been Tested?

• Previewed the README after editing via GitHub UI
• Verified correct Markdown rendering and container setup clarity

Additional Context

Before:

• Heading said “PostgreSQL Container” while using MySQL

After:

• Corrected to “MySQL Container”
• Applied consistent markdown and added emojis for clarity

Checklist:

• My change follows the style guidelines of this repo
• I reviewed my own changes
• Documentation is updated
• No new warnings or errors introduced
• Commit message is clear
• Marked reviewers if needed
• I agree to the Developer Certificate of Origin (DCO)