Generally, when you interact with files (e.g. :e some-file.txt), you are both adding it to the buffer list and loading the contents of the file as a separate buffer. The :bad command allows you to add a file to the buffer list without loading it. For instance, you can add your README.md to the buffer list and leave the current buffer in focus with:

:bad README.md

This command seems particularly useful for scripting the setup of an initial vim environment or preparing for a :bufdo command.