Here are some references for shell script developers, man page creators, README writers, etc. While documentation styles are a bit haphazard and vary with OS and programming language, there are some standards.
For man pages see man-pages(7). What does that mean? You open a terminal window then type:
man 7 man-pages
The Debian Policy Manual says where the different documentation files should be located but not what they should look like.
I'm not going to admit to following these but please post any other IT technical writing style guides you know of. :D