add memo about 'za' and other folding commands
add memo about 'za' and other folding commands

add memo/obvious rec for 'za', useful for someone like me
who hasn't used folding much in vim
but is using workflowish every day
and opens README to remember commands
until committed to memory :)

also threw in a link to the exact part of the Vim wiki that tells you all the commands.
lukaszkorecki/workflowish