docs: Update README.md

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README.md

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   <strong>A Neovim plugin for cycling through checkbox states.</strong>
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+![checkbox-cycle](https://github.com/user-attachments/assets/1476a626-b957-4720-95f0-fb2724404ae1)
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 ## ❓ Why?
 
 Managing checkboxes in markdown files can be tedious, especially when working with to-do lists or task management in documents. Manually typing out or toggling between different checkbox states (unchecked, in-progress, checked, etc.) slows down your workflow. `checkbox-cycle.nvim` simplifies this by allowing you to effortlessly toggle and cycle through custom checkbox states, streamlining task management directly within Neovim.