add deprecation notice

[byennen]

Pull Request Description

Summary:
This pull request updates the README of the @uniswap/widgets package to include a deprecation notice and guidance for developers. The notice informs users that the package is no longer actively supported by Uniswap Labs and encourages them to transition to Uniswap v4 for building custom swap functionality.

Changes:

• Added a deprecation notice at the beginning of the README, clearly stating that the @uniswap/widgets package is no longer supported.
• Recommended using Uniswap v4 and building custom swap components using the latest version of the Uniswap protocol.

Reason for Changes:
The @uniswap/widgets package is no longer actively supported by Uniswap Labs, and the team is recommending developers to move to Uniswap v4 for greater flexibility and customization. This update is intended to save other developers time.

Related Issues:

• N/A

Impact:

• Developers relying on the @uniswap/widgets package should transition to Uniswap v4 for building their own swap functionality.
• The README now clearly communicates the deprecation, helping users make informed decisions about using the package.

[vercel]

@byennen is attempting to deploy a commit to the Uniswap Team on Vercel.

A member of the Team first needs to authorize it.

[0xdevant]

Then for Frontend development should we reference Uniswap Interface to build our custom swap components?