fix(create): Commands added by plugin (through preset) won't have description in README' (#1910)

Author: pksunkara

packages/@vue/cli/lib/util/generateReadme.js

@@ -9,6 +9,7 @@ const descriptions = {
 
 function printScripts (pkg, packageManager) {
   return Object.keys(pkg.scripts).map(key => {
+    if (!descriptions[key]) return ''
     return [
       `\n### ${descriptions[key]}`,
       '```',