docs: fix broken Next.js integration link and add inline setup guide

[tranhoangtu-it]

Problem

The Next.js integration link in the README points to https://github.com/zeit/next.js/tree/canary/examples/with-why-did-you-render which is broken for two reasons:

1. The GitHub organization moved from zeit to vercel
2. The with-why-did-you-render example was removed from the Next.js repository

This was reported in #295.

Solution

• Remove the broken external link
• Add an inline Next.js setup code snippet (Pages Router pattern — the most common usage)
• Link to the existing community discussion (Integration with Next.js 13 app folder? #266) for App Router and advanced setups

Changes

• README.md: replaced dead link with inline wdyr.js setup example and a link to the integration discussion

Fixes #295

[Copilot]

Pull request overview

Updates the documentation to remove a dead Next.js example link and replace it with an inline setup snippet plus a pointer to the existing Next.js integration discussion, addressing the broken-link report in #295.

Changes:

• Removed the broken external Next.js example link (old zeit/next.js URL / removed example).
• Added an inline wdyr.js setup snippet for Next.js.
• Linked to the Next.js integration discussion (#266) for broader/App Router guidance.

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[Copilot]

The README suggests importing wdyr.js as the first import in app/layout.js for the App Router. In Next.js App Router, app/layout.js is a Server Component by default, and importing/initializing why-did-you-render there can cause build/runtime issues (and won’t reliably apply to client components). Consider removing the app/layout.js instruction or changing it to a client-only entry point (e.g., a 'use client' provider/component imported by the layout) and keep the README pointing to the #266 discussion for App Router specifics.

Suggested change

	* **Next.js**: Create a `wdyr.js` file and import it as the **first import** in `pages/_app.js` (Pages Router) or `app/layout.js` (App Router). See the [Next.js integration discussion](https://github.com/welldone-software/why-did-you-render/issues/266) for setup details.
	* **Next.js**: Create a `wdyr.js` file. For the **Pages Router**, import it as the **first import** in `pages/_app.js`. For the **App Router**, initialize it from a client-only entry point (for example, a `'use client'` provider/component) and follow the recommendations in the [Next.js integration discussion](https://github.com/welldone-software/why-did-you-render/issues/266).