It's so common for beginners !
Usually when we start a new project, we focus on the good part (the code), system logic, server configuration and that kind of thing, and completely forget some stuff like documentation, security, scalability, etc...
And Yes! also the README.md is completely forgotten, it's like a self stab, because we are humans and usually forget things, like the command to start the project, restrictions, how to deploy, how feature works, how to run tests and many more. Maybe you will say something like "Ok, I only work on this project, I can remember that kind of commands", but what about the other team members, what about NEW team members? they are going to lose a lot of time checking how to start, stop, test....
The README is going to make your life easier for you and every team member, and ins't a heroic task, it's as simple as created a file named README.md inside the project and that is all.
Even if you start to use the readme file, you can add more interesting things, like build status, deploy status and that kind of icons red/orange/green, unit test coverage and limits.
I used to assume that README was a file located at the root of a software repository. Did you know a README file serves as an index file in any directory of your versioned tree? It is pretty handy if you feel the need to split its content, or if you want to address specific needs for relevant folders of your projects.
And remember, README files are the entry points needs, to be focused in what is really needed.
You can use tools as Dillinger to write it easily.
Here are some examples :