Add note to bundle docs about requiring an experimental Engine build

Signed-off-by: Aanand Prasad <[email protected]>

docs/bundles.md

@@ -50,6 +50,15 @@ Wrote bundle to vossibility-stack.dab
 
 ## Creating a stack from a bundle
 
+> **Note**: Because support for stacks and bundles is in the experimental stage,
+> you need to install an experimental build of Docker Engine to use it.
+>
+> If you're on Mac or Windows, download the “Beta channel” version of
+> [Docker for Mac](https://docs.docker.com/docker-for-mac/) or
+> [Docker for Windows](https://docs.docker.com/docker-for-windows/) to install
+> it. If you're on Linux, follow the instructions in the
+> [experimental build README](https://github.com/docker/docker/blob/master/experimental/README.md).
+
 A stack is created using the `docker deploy` command:
 
 ```bash