Disable BIOS boot support

Hopefully, this will decrease the amount of time that it takes to build
installation ISOs. Additionally, this change allows me to make the
instructions in the README shorter.

README.md

@@ -113,14 +113,6 @@ notes that I have for them:
 	the virtual disk you create for it is large enough to store the “Keep
 	Across Linux Distros!” Syncthing folder.
 
-- Booting from the install medium: Make sure that you boot into UEFI mode. Once
-	you’re at a command prompt, run
-	[this command](https://askubuntu.com/a/162896):
-
-		[ -d /sys/firmware/efi ] && echo UEFI || echo BIOS
-
-	If it outputs “UEFI”, then you’re good.
-
 - Graphical Installation: Skip right to the Manual Installation section. We’re
 going to be doing a manual installation, not a graphical one.
 

src/modules/installation-image.nix

@@ -11,6 +11,8 @@
 		# to download any additional dependencies in order to build the
 		# system configuration.
 		includeSystemBuildDependencies = true;
+		makeBiosBootable = false;
+		makeEfiBootable = true;
 	};
 	users.users.nixos.packages = let
 		pkgCollections = import ../pkgCollections { inherit pkgs lib; };