Add example for v2

[Kishlay-notabot]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

If changing the UI of the default theme, please provide the before/after screenshot:

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• Yes
• No

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The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

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• A convincing reason for adding this feature
• Related documents have been updated
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To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:
Add example file where we can use multiple crop-selection instances in one canvas and download the cropped selections.

[Kishlay-notabot]

@fengyuanchen

[fengyuanchen]

There is one similar example in the official documentation: https://fengyuanchen.github.io/cropperjs/v2/api/cropper-selection.html#multiple