The help for
If [command] is not given the 'shell' option is used.
On that help page, if you move the cursor inside the word "shell" and press
C-] (the control key and the right bracket), it'll take you to the help for the shell setting. Alternatively, you can get there with
It looks like you should be able to add the following to your
You may need to specify the full path to cmder depending on whether it's in your system path.
Also note that the
shell setting is used for executing external commands from vim. I'd recommend reading the help for that setting to make sure it will work as you expect.