fix: True Metal should not be broken!

[arkel-s]

Recent update of Java 21 broke the Dockerfile. The pom.xml file is also broken.
Fixing it, True Metal should never be broken 🤘

Also adding Metal dependency as requested by #36
Cleaned the Redme as requested by #44

[external-torx]

I support this change and I'm doing all the same stuff to my pom.xml locally to get to run but I would prefer to keep the javac instructions in the README on the basis that no one writing/running HelloWorld for the first time should need to learn maven to do it.

[arkel-s]

I support this change and I'm doing all the same stuff to my pom.xml locally to get to run but I would prefer to keep the javac instructions in the README on the basis that no one writing/running HelloWorld for the first time should need to learn maven to do it.

Thanks for having a look @external-torx
Actually I removed javac in the readme but kept the Single File source-code execution which works fine without Maven, as javac is not needed for this simple use case.
java src/main/java/it/nanowar/ofsteel/helloworld/HelloWorldMainLauncherClass.java

See Rendered REAMDE.md

Is it fine for you?

[external-torx]

Looks great to me, but I'm just a spectator, not one of the maintainers of the repo