Added a note with instructions on eslint plugin configuration

Created by: DiegoCardoso

I've installed both Sublime Text and Visual Studio Code in order to see if I needed to add any extra configuration to make eslint work. Since the only editor that I found the issue was Atom, I added just the instruction for the linter-eslint plugin.

Below is the instruction that I added:

Note: if you are using the linter-eslint plugin on Atom, make sure that Use global ESLint installation option is checked.