Add detailed steps for installing Coder using different methods:

- Single CLI for Coder server and client
- Release channels: mainline and stable

Installation methods:

- For Linux/macOS:
  ```sh
  curl -L https://coder.com/install.sh | sh
  ```

- For Windows:
  - Available on [GitHub releases](https://github.com/coder/coder/releases)
  - Visual C++ Runtime required for PostgreSQL
  - Alternatively, use `winget`:
    ```powershell
    winget install Coder.Coder
    ```

Post-install steps:

- Start Coder server:
  ```sh
  coder server
  ```

- Log in to existing deployment:
  ```sh
  coder login https://coder.example.com
  ```

Next steps:

- [Create your first template](../templates/tutorial.md)

- Added a link to the guide for exposing the control plane to other users.
- This helps admins configure their deployments for multi-user access.