This cuts the image size down alot, esspecially if there were lots of
small file deletes.
The fstrim utility is in the util-linux package and should be on
most all systems. fstrim also works with XFS, ext4, btrfs, etc
prodiving the kernel is new enough.
A reduction of 25% or more in size is common.
Change-Id: I269b4416be450369616f9b8e030f84c30e329804
Our docs are very developer focused. Lets create a separate user guide
to help new users get started.
Change-Id: I8a03920e6d3306dd0405177875ea55ccb4b40fea