README.hardware: clarify NFS requirements for edgerouter

You don't need NFS/TFTP for a plain USB setup.

(From meta-yocto rev: 76ea21bdb1448417fb4e2e2f5659c911a30a5026)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

README.hardware

@@ -352,19 +352,22 @@ Setup instructions
 ------------------
 
 You will need the following:
-* NFS root setup on your workstation
-* TFTP server installed on your workstation
 * RJ45 -> serial ("rollover") cable connected from your PC to the CONSOLE
-  port on the board
+  port on the device
 * Ethernet connected to the first ethernet port on the board
 
+If using NFS as part of the setup process, you will also need:
+* NFS root setup on your workstation
+* TFTP server installed on your workstation (if fetching the kernel from
+  TFTP, see below).
+
 --- Preparation ---
 
 Build an image (e.g. core-image-minimal) using "edgerouter" as the MACHINE.
 In the following instruction it is based on core-image-minimal. Another target
 may be similiar with it.
 
---- Booting from NFS root ---
+--- Booting from NFS root / kernel via TFTP ---
 
 Load the kernel, and boot the system as follows: