docs: add permissions and :client-name to getting-started What's Next

Add two missing topics to doc/getting-started.md:

- Permission model: explain deny-by-default, show approve-all usage,
  link to Permission Handling section in API Reference
- :client-name option: show how to identify an application in session config

Both features were added in merged PRs (#18 and #21) but were not
reflected in the getting-started tutorial.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 2 people

doc/getting-started.md

@@ -251,6 +251,32 @@ Now that you have the basics, explore these topics:
 - **[MCP Servers](./mcp/overview.md)** — Connect to external tools via MCP
 - **[Examples](../examples/README.md)** — More working examples
 
+### Permissions (deny-by-default)
+
+The SDK uses a **deny-by-default** permission model. When Copilot requests permission
+to run shell commands, write files, or fetch URLs, the SDK denies all requests unless
+you provide an `:on-permission-request` handler.
+
+Use `approve-all` to permit everything:
+
+```clojure
+(copilot/with-client-session [session {:model "gpt-5.2"
+                                       :on-permission-request copilot/approve-all}]
+  ...)
+```
+
+Or write a custom handler for fine-grained control. See [Permission Handling](./reference/API.md#permission-handling) in the API Reference.
+
+### Identifying Your Application
+
+Pass `:client-name` to identify your application in API requests (included in the User-Agent header):
+
+```clojure
+(copilot/with-client-session [session {:model "gpt-5.2"
+                                       :client-name "my-weather-app"}]
+  ...)
+```
+
 ### Key Concepts
 
 | Concept | Description |