message: docs: delete `--out` option from README
diff: @@ -24,7 +24,7 @@ $ kintone-plugin-packer [OPTIONS] PLUGIN_DIR
  ## Options
  - `--ppk PPK_FILE`: The path of input private key file. If omitted, it is generated automatically into `<Plugin ID>.ppk` in the same directory of `PLUGIN_DIR`.
  -- `--out PLUGIN_FILE`: The path of generated plugin file. The default is `plugin.zip` in the same directory of `PLUGIN_DIR`.
  +- <del>`--out PLUGIN_FILE`: The path of generated plugin file. The default is `plugin.zip` in the same directory of `PLUGIN_DIR`.</del> Not implemented yet.
  ## How to use with `npm run`
  