Document reading ISP proxy static IP via ip_address (#499)

* Document reading ISP proxy static IP via ip_address

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* Use absolute URLs for API reference links

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: dprevoznik

proxies/isp.mdx

@@ -147,3 +147,39 @@ func main() {
 </CodeGroup>
 
 See the [overview](/proxies/overview#bypass-hosts) for full bypass host rules and examples.
+
+## Getting the static IP address
+
+Because an ISP proxy has a static exit IP, you can read that IP once and reuse it — for example, to add it to an IP allowlist. The IP is returned as `ip_address` in the response when you [create a proxy](https://kernel.sh/docs/api-reference/proxies/create-a-proxy) and when you [get a proxy by ID](https://kernel.sh/docs/api-reference/proxies/get-proxy-by-id).
+
+<CodeGroup>
+```typescript Typescript/Javascript
+const proxy = await kernel.proxies.create({
+  type: 'isp',
+  name: 'my-isp-proxy',
+});
+
+console.log(proxy.ip_address);
+```
+
+```python Python
+proxy = kernel.proxies.create(
+    type="isp",
+    name="my-isp-proxy",
+)
+
+print(proxy.ip_address)
+```
+
+```go Go
+proxy, err := client.Proxies.New(ctx, kernel.ProxyNewParams{
+	Type: kernel.ProxyNewParamsTypeIsp,
+	Name: kernel.String("my-isp-proxy"),
+})
+if err != nil {
+	panic(err)
+}
+
+fmt.Println(proxy.IPAddress)
+```
+</CodeGroup>