[DOC]: Ambiguity in .devcontainer README's Docker install step for WSL

### Is this a duplicate?

- [x] I confirmed there appear to be no [duplicate issues](https://github.com/NVIDIA/cccl/issues) for this bug and that I agree to the [Code of Conduct](CODE_OF_CONDUCT.md)

### Is this for new documentation, or an update to existing docs?

Update

### Describe the incorrect/future/missing documentation

While setting up my new Windows workstation and following the .devcontainer README instructions, I found that the way it's currently written implies that installing the VSCode Remote Development Extension Pack would handle installing Docker on its own when in fact, it has to be installed. Perhaps the documentation was written to mean that Docker would automatically be picked up after the remote extension pack was installed.

I'm probably overanalyzing the instructions, but assuming there are others like me that would read it as such, I figured a change like this could be beneficial to merge to main:
```diff
diff --git a/.devcontainer/README.md b/.devcontainer/README.md
index ba6859312..f069ed22b 100644
--- a/.devcontainer/README.md
+++ b/.devcontainer/README.md
@@ -79,9 +79,10 @@ Apart from the initial setup of WSL, the process for using CCCL's Dev Containers
- Windows OS that supports WSL 2 (Windows 11 or newer)
- [Windows Subsystem for Linux v2 (WSL 2)](https://learn.microsoft.com/en-us/windows/wsl/install)
- [Visual Studio Code](https://code.visualstudio.com/) (installed on Windows host)
+- [Docker](https://docs.docker.com/engine/install/)
+ - Required for VSCode / Dev Container integration
- [VSCode Remote Development Extension Pack](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.vscode-remote-extensionpack) (installed on Windows host)
- Includes [Dev Containers](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers) and [WSL](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-wsl) extensions
-- [Docker](https://docs.docker.com/engine/install/) - (Will be installed automatically by the Remote Development extension)

#### GPU Prerequisites (only needed for executing tests that require a GPU)
- Supported NVIDIA GPU
```

If you all agree, then I'll create a PR out of this branch: https://github.com/acosmicflamingo/cccl/tree/docker-wsl-clarification. Otherwise, I'll swiftly close this ticket.

### If this is a correction, please provide a link to the incorrect documentation. If this is a new documentation request, please link to where you have looked.

_No response_