markdown-include is a pip package that can be use with mkdocs.

• Install the python package markdown-include per https://github.com/cmacmackin/markdown-include

• Add the following lines in your mkdocs. Set the base_path to your choice.

markdown_extensions:
  - markdown_include.include:
      base_path: .

• And finally add the contents of one file into another by just doing

{!yourfile!}

For real example, check out the this writeup in github