The other way of loading scripts is by using DO SCRIPT. This time the mission editor don't show a file browse button. Instead you see a (very small) text field to enter the code directly into it. It is only useful for very small script snippets. But we can use it to load a file from your hard drive like this:

dofile('C:/MyScripts/hello-world.lua')
dofile('C:\\MyScripts\\hello-world.lua')
dofile([[C:\MyScripts\hello-world.lua]])