doc: add Support section in README
Add a Support section, borrowing heavily from wp-cli project.
Move stuff about contributing to Node.js to the bottom as vastly more users are interested in using Node.js and getting help with Node.js than contributing to Node.js. Information still belongs, just not at the top. (Many people will know to look in CONTRIBUTING.md anyway.)
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines