@netstu Are you alluding to Structured Data or Schema which you have already set. I would recommend setting the Business Type if you can. The rest here is really down to Google to apply this data for its snippets.
If you want a shortcode to inject something like the following into your meta tag:
<meta name="description" content="Bij Nano Web laat je een professionele website maken die ook nog eens winstgevend is. Ontdek waarom meer dan 200 onderneming bij ons klant zijn. ★★★★★" />
… then there is nothing in the plugin code that exists to perform this action. For a shortcode to execute, the SEO plugin would need to support this (unlikely and inadvisable) or I would need to add something to take over the handling of the website’s meta data…
In your case, you can simply add the HTML star entities into the page’s description (like in the example) using an SEO plugin.
Personally, I would avoid adding this unless it is specifically relevant to the page’s content. I don’t think it will have any positive effect on your SEO if you just add it everywhere.
I am marking this as resolved as it is outside of the plugin’s functionality. Also I don’t feel there is a need to add new functionality to perform such an action.
I hope this answers your question.
Additionally – for your design, I would recommend using the Narrow theme.