Add the 'cat' compression option to the list for consistency's sake as it was
mentioned in the comment above.  Also sorts the various options by their
compression efficiency based on compressing the fallback image by each of the
respective methods (default options).

 % ls -Sl
 17140224 initramfs-linux-fallback.img
 8375766 initramfs-linux-fallback.img.lzo
 6039365 initramfs-linux-fallback.img.gz
 5394818 initramfs-linux-fallback.img.bz2
 4058536 initramfs-linux-fallback.img.xz
 4057855 initramfs-linux-fallback.img.lzma

--- a/mkinitcpio.conf	2013-07-18 14:23:43.000000000 -0400
+++ b/mkinitcpio.conf	2013-11-03 02:52:35.974235044 -0500
@@ -54,11 +54,12 @@
 # COMPRESSION
 # Use this to compress the initramfs image. By default, gzip compression
 # is used. Use 'cat' to create an uncompressed image.
+#COMPRESSION="cat"
+#COMPRESSION="lzop"
 #COMPRESSION="gzip"
 #COMPRESSION="bzip2"
-#COMPRESSION="lzma"
 #COMPRESSION="xz"
-#COMPRESSION="lzop"
+#COMPRESSION="lzma"
 
 # COMPRESSION_OPTIONS
 # Additional options for the compressor