When you open a project, Codio will search for a file called README.md in the root of your project file tree. If it finds the file, it will open and display it in preview mode. A read me file may have been automatically created for you when you created the project.
The README.md file should be composed using Markdown format, a simplified markup language used to format plain text.
You can switch to edit mode by clicking on the pencil as shown below.
You can switch back to preview mode by clicking on the symbol shown below located in the upper right corner of your workspace.
Here is a reference for Markdown: