Properly document the Dockerfile requirements for the scripts

[felipecrs]

For example, node-debian.sh seems to require:

ARG NODE_VERSION="lts/*"
ENV NVM_DIR=/usr/local/share/nvm
ENV NVM_SYMLINK_CURRENT=true \
  PATH=${NVM_DIR}/current/bin:${PATH}

In order to work properly.

At least until we have microsoft/vscode-remote-release#3593, otherwise the scripts would take care of it by themselves.

[Chuxel]

@felipecrs Yep, agreed - Had this on the list here: #560. Can reuse this as the specific item for docs.

[Chuxel]

This is complete. Scripts will also reference the location of the doc for the script.

[felipecrs]

The new docs are very nice. It's very clear now how to use those scripts. :-D

Thank you @Chuxel!