Any free and reliable app to display Markdown documents in macOS? Sometimes we add a file readme.txt in our folder for notes or things to know about.

Using Markdown, it is pretty easy to make it into a nicely formatted document. Can we write a README.md and can use any free and reliable app and use the Mac to read it?

(So far I know Atom has a Markdown-preview which can be activated by using the keyboard shortcut Control + Shift + M, but if there is a one click preview app, it'd be the best. There is a Quick Look plug-in, but I am wondering if I should alter my OS? If there is a trustworthy app that can do it, it'd be best).
Xcode : if you already use it.
Sublime text:  https://www.sublimetext.com you can also install plugins suitable for you. It is much smaller than Xcode, doesn't exceed 100 MB, despite several packages. 

Install packages using cmd+shift+p and then typing "install package". Then type the name of the package, it would show you the webpage of the developer where you can find the documentation. 
VSCode: with some extensions it can work.