docs(next): update homepage & init setup toturial (#1386)

apps/next/src/content/docs/llamaindex/starter/getting-started.mdx

+---
+title: Getting Started
+description: We support multiple JS runtime and frameworks, bundlers.
+---
+
+<Cards>
+  <Card title="Node.js" href="/docs/llamaindex/starter/node" />
+  <Card title="Vite" href="/docs/llamaindex/starter/vite" />
+  <Card
+    title="Next.js (React Server Component)"
+    href="/docs/llamaindex/starter/next"
+  />
+  <Card title="Cloudflare Worker" href="/docs/llamaindex/starter/cloudflare" />
+</Cards>

apps/next/src/content/docs/llamaindex/starter/meta.json

+{
+  "title": "Starter",
+  "description": "The starter guide",
+  "defaultOpen": true,
+  "pages": ["getting-started", "next", "node"]
+}

apps/next/src/content/docs/llamaindex/starter/next.mdx

+---
+title: With Next.js
+description: In this guide, you'll learn how to use LlamaIndex with Next.js.
+---
+
+Before you start, make sure you have try LlamaIndex.TS in Node.js to make sure you understand the basics.
+
+<Card
+  title="Getting Started with LlamaIndex.TS in Node.js"
+  href="/docs/llamaindex/starter/node"
+/>
+
+## Differences between Node.js and Next.js
+
+Next.js is a React framework that has both server side compatibility and client side compatibility.
+This means that you need to be careful when using LlamaIndex.TS in Next.js.
+Don't leak the import data like API keys to the client side.
+
+Also, in Next.js, there is build time and runtime. Some computations can be done at build time like Document embedding could be done at build time for better performance.
+LlamaIndex.TS has lots of upstream dependencies, some of them are not compatible with Next.js.
+
+You might need to use `withNext` to make sure that LlamaIndex.TS works well with Next.js.
+
+```js
+// next.config.mjs / next.config.ts
+import withLlamaIndex from "llamaindex/next";
+
+/** @type {import('next').NextConfig} */
+const nextConfig = {};
+
+export default withLlamaIndex(nextConfig);
+```
+
+If you see any dependency issues, you are welcome to open an issue on the GitHub.

apps/next/src/content/docs/llamaindex/starter/node.mdx

+---
+title: With Node.js/Bun/Deno
+description: In this guide, you'll learn how to use LlamaIndex with Node.js, Bun, and Deno.
+---
+
+## Adding environment variables
+
+By default, LlamaIndex uses OpenAI provider, which requires an API key. You can set the `OPENAI_API_KEY` environment variable to authenticate with OpenAI.
+
+```shell
+export OPENAI_API_KEY=your-api-key
+```
+
+Or you can use a `.env` file:
+
+```shell
+echo "OPENAI_API_KEY=your-api-key" > .env
+node --env-file .env your-script.js
+```
+
+<Callout type="warn">Do not commit the api key to git repository.</Callout>
+
+For more information, see the [How to read environment variables from Node.js](https://nodejs.org/en/learn/command-line/how-to-read-environment-variables-from-nodejs).
+
+## TypeScript support
+
+LlamaIndex.TS is written in TypeScript and provides type definitions.
+We recommend using [tsx](https://www.npmjs.com/package/tsx) to run TypeScript scripts.
+
+```shell
+npx tsx my-script.ts
+# or
+node --import tsx my-script.ts
+```

apps/next/src/lib/const.ts

+// when we are ready, change to /docs/llamaindex
+export const DOCUMENT_URL = 'https://legacy.ts.llamaindex.ai/'