GPU: vulkan fallback

src/data/config.txt

@@ -159,6 +159,7 @@
 # Sets an user specific path to a library to load.
 # Must be a valid path to a library.
 #--lib-PCI /usr/lib/libpci.so
+#--lib-vulkan /usr/lib/libvulkan.so
 #--lib-X11 /usr/lib/libX11.so
 #--lib-Xrandr /usr/lib/libXrandr.so
 #--lib-gio /usr/lib/libgio-2.0.so

src/data/help.txt

@@ -87,6 +87,7 @@ Key options: Provide a custom key for an output
 
 Library options: Set the path of a library to load
    --lib-PCI <path>
+   --lib-vulkan <path>
    --lib-X11 <path>
    --lib-Xrandr <path>
    --lib-gio <path>