This is a quick how-to of how to set a custom resolution and/or enable windowed mode.

At the time of writing this, you need to do this by editing the configuration file as the in-game menus lack the options of setting these values.
Sounds harder than it is ;-)

• First, find the following file:

• Open the file in your favourite text editor.

There is two sections/blocks of values that are of interest now:
and

The names of the values are pretty self explanatory, with the first block of values you set the resolution you want to have and with the second one you set the fullscreen/windowed mode.

With the resolution, set it for both value pairs, the "ResolutionSize...." ones as well as the "LastUserConfirmedResolutionSize...." ones.

It gets a bit more interesting with the screenmode settings.
First off, set all three values to the same setting, possible values are:

• 0 - Fullscreen
  
• 1 - Borderless Window "Fullscreen"
  
• 2 - Windowed

Save the file, launch the game and enjoy, that's it :-)