[skip ci] Add section on devcontainer customization.

.devcontainer/README.md

@@ -81,6 +81,15 @@ CCCL provides environments for both the oldest and newest supported CUDA version
 
 Look in the [`.devcontainer/`](.) directory to see the available configurations.The top-level [`devcontainer.json`](./devcontainer.json) serves as the default environment. All `devcontainer.json` files in the `cuda<CTK_VERSION>-<HOST-COMPILER>` sub-directories are derived from this top-level file, just with different base images for the different CUDA and host compiler versions.
 
+
+## VSCode Customization
+
+By default, CCCL's Dev Containers come with certain VSCode settings and extensions configured by default as can be seen in the [`devcontainer.json`](./devcontainer.json) file. This can be further customized by users without needing to modify the `devcontainer.json` file directly.
+
+For extensions, the [`dev.containers.defaultExtensions` setting](https://code.visualstudio.com/docs/devcontainers/containers#_always-installed-extensions) allows listing extensions that will always be installed.
+
+For more general customizations, VSCode allows using a dotfile repository. See the [VSCode documentation](https://code.visualstudio.com/docs/devcontainers/containers#_personalizing-with-dotfile-repositories) for more information.
+
 ## GitHub Codespaces
 
 [![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/NVIDIA/cccl?quickstart=1&devcontainer_path=.devcontainer%2Fdevcontainer.json)