Add javafx:help goal

[Colnup]

[Suggested labels] : question,enhancement

Hi all :wave:

I'm new to using javafx with maven. I saw on the internet that it was a standard for a module to provide a help goal that would display help text for all the goals.

It would be useful if beginners could run the command mvn javafx:help and get a small help for each goal (currently only jlink and run).

Let me know whether this is a good idea or not, I'm not familiar enough with maven and javafx to know.