gatsby-remark-embed-runkit

npm install gatsby-remark-embed-runkit
// Requires gatsby-transformer-remark
npm install gatsby-transformer-remark

Add to your gatsby-config.js

{
      resolve: 'gatsby-transformer-remark',
      options: {
        plugins: [
          "gatsby-remark-embed-runkit",
      }
}

Add your nice url inside backticks

https://runkit.com/yamoo/const

and boom you get an embed