add documentation clarifying behavior of VOLUME instruction
@@ -906,6 +906,10 @@ This Dockerfile results in an image that causes `docker run`, to
create a new mount point at `/myvol` and copy the `greeting` file
into the newly created volume.
+> **Note**:
+> If any build steps change the data within the volume after it has been
+> declared, those changes will be discarded.
+
> **Note**:
> The list is parsed as a JSON array, which means that
> you must use double-quotes (") around words not single-quotes (').
