Directory mu-plugins or just plugins?

Hello, I have just installed Supporter.

In instructions, there was written that I had to install some files in “mu-plugins” folder, which I hadn’t created. So I created this folder and upload the files into that. But plugin wasn’t activated. Than I realized that mu-plugins isn’t necessary and put these files in wp-content/plugins folder where other multisite/singlesite plugins are too and everything works fine now.

Is it correct the way I installed it? Will it cause any troubles in future?