Add tooltip

[dutiyesh]

• Add tooltip that displays current value of slider while it's being dragged.
• Add an option to format tooltip value.
• Add tests to ensure tooltip rendering if enabled.
• Add story in storybook.
• Update README file with tooltip documentation and example.

Default tooltip:

Tooltip with formatted value:

[dutiyesh]

What about 'Toast' as a name?

[ljharb]

lol I’m not sure how that makes sense

[dutiyesh]

Toast is a term used in Android. Definition: A toast provides simple feedback about an operation in a small popup.

In our case, we are providing a feedback for user's slider drag operation.

[ljharb]

I doubt that term has any such meaning outside of an android context; let's keep the bikeshed going til we find something more universal :-)

[dutiyesh]

What if we name it related to rheostat itself? Like 'meter'. As it will provide rheostat's meter reading.