Introduce a few user arguments

lib/commands/sign.js

@@ -13,6 +13,10 @@ module.exports.builder = (yargs) => {
             describe: 'Challenge to sign',
             type: 'string'
         })
+        .option('p', {
+            describe: 'will post signature to response endpoint',
+            type: 'boolean'
+        })
         .demandOption(['challenge'])
         .argv;
 }