docs: mention Tailwind-style CSS requirement for wallet UI

[gupta-8]

Summary

This PR updates the README to document the styling requirements for the wallet
connection UI. It clarifies that the modal relies on Tailwind-style utility
classes and may appear broken or misaligned if those styles are not present.

Changes

• Add a new "Styling & Wallet Connection UI" section to README.md
• Explain that including Tailwind (or equivalent utility CSS) is necessary
  for correct wallet modal layout and styling

Motivation

This addresses the confusion reported in #131, where the wallet connection UI
appears broken until Tailwind CSS is added. By documenting this requirement,
integrators can quickly resolve the issue without trial-and-error.

Closes #131

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