docs: Document custom endpoint support in Vercel AI SDK (#579)

Author: lavanya-gunreddi

public-endpoints/ai-sdk.mdx

@@ -63,6 +63,49 @@ const runpod = createRunpod({
 | `baseURL` | Base URL for API requests | `https://api.runpod.ai/v2` |
 | `headers` | Custom HTTP headers to include with requests | `{}` |
 
+## Using custom endpoints
+
+You can use your own [Serverless endpoints](/serverless/overview) with the AI SDK. This is useful when you've deployed a custom model or want to use a specific endpoint you've created.
+
+### Using endpoint IDs
+
+Pass your Serverless endpoint ID directly as the model identifier:
+
+```typescript
+import { runpod } from "@runpod/ai-sdk-provider";
+import { generateText, experimental_generateImage as generateImage } from "ai";
+
+// Use a custom chat endpoint
+const { text } = await generateText({
+  model: runpod("your-endpoint-id"),
+  prompt: "Hello, how are you?",
+});
+
+// Use a custom image endpoint
+const { image } = await generateImage({
+  model: runpod.image("your-image-endpoint-id"),
+  prompt: "A beautiful sunset",
+});
+```
+
+The SDK resolves your endpoint ID to `https://api.runpod.ai/v2/{endpointId}` automatically.
+
+### Using Console URLs
+
+Copy an endpoint URL directly from the Runpod Console and use it as the model identifier:
+
+```typescript
+import { runpod } from "@runpod/ai-sdk-provider";
+import { experimental_generateImage as generateImage } from "ai";
+
+const { image } = await generateImage({
+  model: runpod.image("https://console.runpod.io/serverless/user/endpoint/abc123xyz"),
+  prompt: "A serene mountain landscape",
+});
+```
+
+The SDK extracts the endpoint ID from the Console URL and routes requests to your endpoint.
+
 ## Text generation
 
 ### Basic text generation