What to write in "README.md" (GitHub)?

Question

GitHub

I've been digging into other people's projects here, and looking at how they describe README
Someone simply writes:

1. npm install
   
2. npm run serve
   

Someone starts with git clone ...
And some don't write anything at all, they just have a bunch of text with pictures ...

In general, are there any "basic" rules for filling "README.md" ?
Thank you!

Answer 1

There are no rules.
Usually they indicate:
1. Installation
2. Description
3. Documentation
4. Authors
5. License
Your repository, your rules, do as you wish.