The NOW extension name for readme files is a bit of a joke. The reason for NOW - Readme File extensions comes down to the simple fact that people generally don't read the readme files. So they skip reading vital information, and then they pester the developers and the help desk with questions that they would already know the answer to if they had just bothered to skim the readme.
So when you see a readme file called ReadMe.NOW, it grabs your attention and makes you want to open that file and read it. The extension name is more of a humorous reminder of how important the readme file is than anything. The file is still just a regular old text file, it's just words on the screen, but with NOW as the extension name, users are more likely to actually read it.
Readme files contain vital information if you want to get the most out of your new software purchase. It's important to take the time to actually read through them before you get started using your software, and the NOW extension is a great, humorous way to remind us that hey, what's in this file is actually pretty important.