Add prop to mark field as required

[mfrazie2]

• Add prop reference to README and interface
• Add storybook entry
• Add prop to mark field as required

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🔍 Inspect: https://vercel.com/srigar/multiselect-react-dropdown/BDJFgwyeKF9GhQuW2aTiAnkpCq88
✅ Preview: https://multiselect-react-dropdown-git-fork-mfrazie2-mark-17d584-srigar.vercel.app

[mfrazie2]

There is no feedback provided to the end user they are missing information. Open to suggestions on the best way to do so.

[mfrazie2]

Leveraging the in browser alert for empty required fields