docs: add custom API use cases (#8445)

docs/api/index.md

@@ -1,4 +1,26 @@
-Get started with Coder API:
+Get started with the Coder API:
+
+## Quickstart
+
+Generate a token on your Coder deployment by visiting:
+
+```sh
+https://coder.example.com/settings/tokens
+```
+
+List your workspaces
+
+```sh
+# CLI
+curl https://coder.example.com/api/v2/workspaces?q=owner:me \
+-H "Coder-Session-Token: <your-token>"
+```
+
+## Use cases
+
+See some common [use cases](../admin/automation.md#use-cases) for the REST API.
+
+## Sections
 
 <children>
   This page is rendered on https://coder.com/docs/coder-oss/api. Refer to the other documents in the `api/` directory.