Users of unofficial kernels must enable devtmpfs support

As of udev-176, the Arch Linux userspace tools will no longer be able to boot kernels without devtmpfs support.

The official Arch kernels (kernel26-lts and linux) have both had devtmpfs support for a long time, so only people who compile their own kernels are potentially affected by this change.

More information about the kernel options required by udev is available in the udev README.