Document supported Node versions

[kibertoad]

Currently it is very unclear which Node versions are supported. CI is executed on 12 and 14, but quick glance at a source code seems to indicate that it is likely to work on Node 6+ as well. Would it be possible to clarify that in documentation and/or package.json engine entry?

[jorgebucaran]

Officially supported versions are 10 through 16, but you're right, it should work with 6 too! I have no plans to break compatibility with older Nodes, but supporting 6 is not a goal.

If this is causing confusion, a note in the documentation would be fine.