ReadMe has pre-built widgets for you to use, that you can drag and drop on the right side of the content editor.
The header widget will create an h1 header for you.
The code sample widget allows you to write styled code samples, and you should be able to add as many tabs as you need for different languages.
The callout widget can be used to display different callouts to give your users warnings or cautions.
This is a callout!
Use this widget to upload an image and choose how you want to scale it.
This widget is a simple way to embed content from YouTube, Github Gists, JSFiddles, PDFs, Google Slides and more, just provide the link and you should be set.
Some embeds may not work well with this, such as vimeo videos. In that case you should use the HTML/CSS widget to embed.
Lastly you can add custom HTML/CSS for your content using this widget if you need anything else! This can be used for more customized embeds or widgets that you may want.