Update READMEs and add a CONTRIBUTING.md (#1079) #728

Job	Run time
copyright	3m 13s
build	5m 7s
checkstyle	3m 25s
shellcheck	3m 8s
spotbugs	5m 19s
javadoc	5m 58s
tests/cli-linux	5m 15s
cli/linux-amd64	4m 33s
tests/cli-functional-linux	6m 35s
vscode-ext	5m 49s
cli/windows-amd64	5m 23s
tests/archetype-linux	4m 42s
cli/darwin-amd64	6m 1s
tests/linker-linux	4m 44s
tests/others-linux	6m 6s
tests/cli-windows	6m 34s
tests/cli-functional-windows	7m 28s
tests/archetype-windows	5m 45s
tests/linker-windows	5m 27s
tests/others-windows	7m 18s
cli/binaries	5s
tests/results	3s
gate	1s
	1h 47m 59s

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