import { Command } from "https://dotland.deno.dev/x/cliffy@v0.11.1/mod.ts";
Add new option (flag).
Parameters
Flags string like: -h, --help, --manual requiredArg:string [optionalArg: number] [...restArgs:string]
optional
opts: ICommandOption | IFlagValueHandlerFlag options or custom handler for processing flag value.