Warn for missing `composer.json` file

[ernilambar]

If plugin contains valid vendor folder generated by composer then it is recommended to add composer.json file in the plugin.

Using composer but could not find composer.json file

We noticed that your plugin is using Composer to handle library dependencies, that's great as it will help maintaining and updating your plugin in the future while avoiding collisions with other plugins that are using same libraries.

The composer.json file describes the dependencies of your project and may contain other metadata as well. It's a small file that typically can be found in the top-most directory of your plugin.

As one of the strengths of open source is the ability to review, observe, and adapt code, we would like to ask you to include that file in your plugin, even if it is only used for development purposes. This will allow others to exercise the open source freedoms from which we all benefit.