vim: visual editor improved
https://vimsheet.com/
https://www.howtogeek.com/102468/a-beginners-guide-to-editing-text-files-with-vi/
https://www.openvim.com/tutorial.html
https://ryanstutorials.net/linuxtutorial/vi.php
https://cheatography.com/nwilde/cheat-sheets/vim/