Rewrite README in markdown format so

it looks nice at https://github.com/freenas/freenas

README → README.md

+# Building FreeNAS
+
 To build the system (experts only):
 
-Requirements:
+## Requirements:
 
-- Your build environment must be FreeBSD 9.2-RELEASE (building on
+* Your build environment must be FreeBSD 9.2-RELEASE (building on
   FreeBSD 10 or 11 is not supported at this time).
 
-- an amd64 capable processor.  8GB of memory, or an equal/greater amount
+* an amd64 capable processor.  8GB of memory, or an equal/greater amount
   of swap space, is also required
 
-- You will need the following ports/packages when compiling anything
+* You will need the following ports/packages when compiling anything
   FreeNAS-related:
-  - ports-mgmt/poudriere-devel
-  - devel/git
-  - sysutils/cdrtools
-  - archivers/pxz
-  - lang/python (2.7 or later, with THREADS support)
-  - emulators/virtualbox-ose
-  - sysutils/grub2-pcbsd
-  - sysutils/xorriso
+  * ports-mgmt/poudriere-devel
+  * devel/git
+  * sysutils/cdrtools
+  * archivers/pxz
+  * lang/python (2.7 or later, with THREADS support)
+  * emulators/virtualbox-ose
+  * sysutils/grub2-pcbsd
+  * sysutils/xorriso
   (and all the dependencies that these ports/pkgs install, of course)
 
-Building the System Quickstart Flow:
+## Building the System Quickstart Flow:
 
-- Checking out the code from git:
+* Checking out the code from git:
 
+```
 % cd /path/to/your-build-filesystem
 % git clone git://github.com/freenas/freenas.git
 % cd freenas
+```
 
-- Build it
+* Build it
 
+```
 % make git-external
 % make checkout
 % make release
+```
 
-- Updating the source tree, to pull in new source code changes
+* Update the source tree, to pull in new source code changes
 
+```
 % make update
+```
 
 This will also fetch TrueOS and ports for the build from github.
 
-The End Result:
+## The End Result:
 
 If your build completes successfully, you'll have both 32 and 64 bit
 release products in the release_stage directory.  You will also have