so all it's saying is open README.md and add something to it then save. Are you getting hung up with "use code ." as the example?
literally all you have to do is open the readme, add something to it like "hello world" or whatever, save it, do git add . then git commit -m "edited README.md" or something. git push. done.
IF you haven't made a README.md yet then in your terminal just do "touch README.md" within your repo, then using whatever editor you use open it and do the above.