Resize rootfs on Pi

README

Check your partitions. You should have 3(1, 2 and 5)

fdisk -l /dev/mmcblk0

Time to resize partitions to occupy the complete SD card.

fdisk /dev/mmcblk0

Now delete extended, logical. Create extended, logical.

sync
reboot
resize2fs /dev/mmcblk0p5

Check whether changes have taken place

df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        15G  795M   14G   6% /
devtmpfs         83M     0   83M   0% /dev
tmpfs           231M     0  231M   0% /dev/shm
tmpfs           231M  244K  231M   1% /run
tmpfs           231M     0  231M   0% /sys/fs/cgroup
tmpfs           231M     0  231M   0% /tmp
/dev/mmcblk0p1   90M   24M   67M  27% /boot

For a 16 Gb SD card, you'll see something like this.
Update

pacman -Syu

Now we have a basic Arch Linux running on Pi.