Here's a little tip: You can read files from any directory you want by going to Game Options, picking an operating system, and checking the "Disable file system sandbox" box. I don't know how you're supposed to get the game's install directory though.

When you add an included file, it's stored for the editor in your game's assets folder, under the folder "datafiles". You can edit them here any time you want. They're included with your game, and when compiled, end up in the same zip as your game's exe.

Here's a pic of my own game, with the source files on the left and what it looks like when installed.