usage function
void
usage()
Implementation
void usage() {
stdout.writeln('Usage:'
'\nenv-gen <cmd> [flags]'
'\ncmd'
'\n\tinitialize\t\tcreates template env file and corresponding directories'
'\n\t<environment>\t\tstring representing an environment from the env.json'
'\n\thelp\t\t\toutputs this usage help'
'\nflags'
'\n\t-v\t\t\tturns on verbose logs'
'\n\t-f <path>\t\tdefine alternate env.json file to use'
'\n\t-e\t\tuse to output an additional .env file'
'\n\t-o <path>\t\tdefine alternate output filepath for env.dart'
'\n\t-h\t\t\toutputs this usage help');
}