UefiCpuPkg VTF0: Rename README to ReadMe.txt, add nasm version

* Rename README to ReadMe.txt
* Document that nasm 2.03 or newer is required for building VTF0

Signed-off-by: ydong10
Reviewed-by: jljusten


git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12384 6f19259b-4bc3-4df7-8a09-765794883524

UefiCpuPkg/ResetVector/Vtf0/ReadMe.txt

@@ -0,0 +1,41 @@
+
+=== HOW TO USE VTF0 ===
+
+Add this line to your FDF FV section:
+INF  RuleOverride=RESET_VECTOR USE = IA32 UefiCpuPkg/ResetVector/Vtf0/Bin/ResetVector.inf
+(For X64 SEC/PEI change IA32 to X64 => 'USE = X64')
+
+In your FDF FFS file rules sections add:
+[Rule.Common.SEC.RESET_VECTOR]
+  FILE RAW = $(NAMED_GUID) {
+    RAW RAW                |.raw
+  }
+
+=== VTF0 Boot Flow ===
+
+1. Transition to IA32 flat mode
+2. Locate BFV (Boot Firmware Volume) by checking every 4kb boundary
+3. Locate SEC image
+4. X64 VTF0 transitions to X64 mode
+5. Call SEC image entry point
+
+== VTF0 SEC input parameters ==
+
+All inputs to SEC image are register based:
+EAX/RAX - Initial value of the EAX register (BIST: Built-in Self Test)
+DI      - 'BP': boot-strap processor, or 'AP': application processor
+EBP/RBP - Pointer to the start of the Boot Firmware Volume
+
+=== HOW TO BUILD VTF0 ===
+
+Dependencies:
+* Python 2.5~2.7
+* Nasm 2.03 or newer
+
+To rebuild the VTF0 binaries:
+1. Change to VTF0 source dir: UefiCpuPkg/ResetVector/Vtf0
+2. nasm and python should be in executable path
+3. Run this command:
+   python Build.py
+4. Binaries output will be in UefiCpuPkg/ResetVector/Vtf0/Bin
+