The vim command :read (or shorter :r) allows you to input anything from a file into the current buffer. Useful if you want to copy things from another file. For example, the following command :read template.md will load the entire content of the file template.md into the buffer.
You can even combine it with the ! command to instead output the result of the shell command. E.g. :r ! ls, will put the output of ls, the list of all files and directories in the current folder, into the buffer.