added README for the "caption" component

[juanmaguitar]

What?

As part of #22891 this PR adds a README.md for this component with some guidance to use.

Why?

Because each component need to have a reference for WordPress developers

How?

By creating a README w/ at least some basic guidance about how to use it

[juanmaguitar]

@derekblank as you seem to be the main developer that has been involved in the work of this component I would appreciate your review and any additions in the README you may consider useful for developers using this component

[derekblank]

LGTM.

[derekblank]

Suggested change

	The `Caption` component renders the [caption part](https://wordpress.org/documentation/article/gallery-block/#caption) of some blocks (image, gallery...)
	This component encapsulates the "caption" behaviour and styles over a `<RichText>` so it can be used in other components such as the `BlockCaption` component
	## Table of contents
	1. [Development guidelines](#development-guidelines)
	2. [Related components](#related-components)
	## Development guidelines
	### Usage
	Renders a Caption area
	```jsx
	import { Caption } from '@wordpress/block-editor';
	const BlockCaption = ( {
	onBlur,
	onChange,
	onFocus,
	isSelected,
	shouldDisplay,
	text,
	insertBlocksAfter,
	} ) => (
	<View >
	<Caption
	isSelected={ isSelected }
	onBlur={ onBlur }
	onChange={ onChange }
	onFocus={ onFocus }
	shouldDisplay={ shouldDisplay }
	value={ text }
	insertBlocksAfter={ insertBlocksAfter }
	/>
	</View>
	);
	```
	### Props
	The properties `isSelected`, `onBlur`, `onChange`, `onFocus`, `shouldDisplay`, `value`, `insertBlocksAfter` of this component are passed directly to their related props of its inner `<RichText>` component ([see detailed info about component's props](https://github.com/WordPress/gutenberg/blob/HEAD/packages/block-editor/src/components/rich-text/README.md))
	## Related components
	Caption components is mostly used by the [`BlockCaption`](https://github.com/WordPress/gutenberg/blob/HEAD/packages/block-editor/src/components/block-caption) component
	The `Caption` component renders the [caption part](https://wordpress.org/documentation/article/gallery-block/#caption) of some blocks (image, gallery...).
	This component encapsulates the "caption" behaviour and styles over a `<RichText>` so it can be used in other components such as the `BlockCaption` component.
	## Table of contents
	1. [Development guidelines](#development-guidelines)
	2. [Related components](#related-components)
	## Development guidelines
	### Usage
	Renders a Caption area:
	```jsx
	import { Caption } from '@wordpress/block-editor';
	const BlockCaption = ( {
	onBlur,
	onChange,
	onFocus,
	isSelected,
	shouldDisplay,
	text,
	insertBlocksAfter,
	} ) => (
	<View >
	<Caption
	isSelected={ isSelected }
	onBlur={ onBlur }
	onChange={ onChange }
	onFocus={ onFocus }
	shouldDisplay={ shouldDisplay }
	value={ text }
	insertBlocksAfter={ insertBlocksAfter }
	/>
	</View>
	);

Props

The properties isSelected, onBlur, onChange, onFocus, shouldDisplay, value, insertBlocksAfter of this component are passed directly to their related props of its inner <RichText> component (see detailed info about component's props).

Related components

Caption components are mostly used by the BlockCaption component.

[derekblank]

Hey @juanmaguitar, thanks for adding the docs! I just added one really minor suggestion to add punctuation at the end of the sentences to match the writing style of the other README files. Feel free to include it or not as you wish. Otherwise, approved. 🚀

[github-actions]

Flaky tests detected in 2540a7f.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/5424201731
📝 Reported issues:

• [Flaky Test] Pick the additional variation in the inserted Columns block #47057 in specs/editor/plugins/block-variations.test.js