Add a list of supported case changing operations to `README.md`

[Korb]

What improvement do you think would an existing feature or tool in DevToys?

Documentation.

Solution/Idea

As I understand from the issues, the application supports many case conversion schemes, but the README.md does not mention the word "case" even once. This is an important functionality, and I suggest considering the possibility of a more complete list of the capabilities of the application.

Comments

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