Required node version is not documented

This project requires `gulp ^3.9.1`, which is not compatible with the latest version of node (v19) or anything after v11.

It would be great if the supported version of node is documented (Dockerfile uses v11), but there is no lts for v11.

The following node lts version seems to work:
```
lts/dubnium -> v10.24.1
```
