Update README.md for Monostate design pattern

[jnniu-n]

Update README.md for monostate design pattern

• Fully explain monostate design pattern.
• Update #2246

Pull request description

• Update Readme.md file in monostate

For detailed contributing instructions see https://github.com/iluwatar/java-design-patterns/wiki/01.-How-to-contribute

[sonarqubecloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[stale[bot]]

Closed due to inactivity. Thank you for your contributions.

[iluwatar]

Looks good! Thank you for the contribution 🎉

@all-contributors please add @jnniu-n for docs

[allcontributors[bot]]

@iluwatar

I couldn't determine any contributions to add, did you specify any contributions? Please make sure to use valid contribution names.

@jnniu-n already contributed before to doc

[sonarqubecloud[bot]]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)
B Maintainability Rating on New Code (required ≥ A)

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