Update

README.md

 ### About
 
-NomadBSD is a live system for flash drives, based on FreeBSD.
+NomadBSD is a persistant live system for flash drives, based on FreeBSD.
 
 ### Screenshots
 ![](http://nomadbsd.org/screenshots/nomadbsd-1.3-RC1-ss1.png)
 
 ### Requirements for building the image
-A recent FreeBSD system
+A recent FreeBSD system with at least 40GB free disk space. The build machine's
+major FreeBSD version must be >= the base system's major version of the image
+you want to build. If you're building the image on a system with ZFS, the build
+might fail due to a problem with the size calculation for the root file system.
+It's best to run a FreeBSD system with UFS in a virtual machine for the build.
 
 ### Requirements for running NomadBSD
-* A 4GB (or more) flash drive
+* A >= 5GB flash drive
 * A (amd64/i386) system with a 1.2GHz CPU and 1G of RAM should be able to run
 NomadBSD decently.
 
 ### Building the image
 By default, the build script builds a 64-bit (amd64) image. For a 32-bit (i386)
-image, set ````ARCH=i386```` in ````build.cfg````.
+image, or a Mac image set `ARCH=i386` or `ARCH=mac` accordingly in `build.cfg`.
+ARCH can also be defined via the `-a` option.
 
 ~~~ csh
 # ./build all
 ~~~
 
-If you want to build an image for Mac, define ````-m````
-~~~ csh
-# ./build -m all
-~~~
-
 If something went wrong, you can resume the build after locating and fixing
 the problem that caused the build to stop.
 ~~~ csh