docs: add Docker installation option for OpenCode

packages/web/src/content/docs/index.mdx

@@ -112,6 +112,12 @@ You can also install it with the following commands:
   mise use --pin -g ubi:sst/opencode
   ```
 
+- **Using Docker**
+
+  ```bash
+  docker run -it --rm ghcr.io/sst/opencode
+  ```
+
 Support for installing OpenCode on Windows using Bun is currently in progress.
 
 You can also grab the binary from the [Releases](https://github.com/sst/opencode/releases).