Tweaks to the comments in the clang/llvm demo.

Author: Jonathan Rocher

llvm_clang_demo.c

@@ -1,6 +1,23 @@
 /* This test file is used to demo how to compile C down to the LLVM Intermediate 
 Representation (LLVM-IR). To do so compile it with 
-clang llvm_clang_demo.c -c -emit-llvm -S -o llvm_clang_demo.ll
+$ clang llvm_clang_demo.c -c -emit-llvm -S -o llvm_clang_demo.ll
+   -c for just compiling
+   -S to generate a human readable file instead of binary bytecode
+
+Look at the resulting ll file and look at it again once it has been simplified 
+with the LLVM optimizer :
+$ opt-3.0 -S -O3 llvm_clang_demo.ll
+generates a simplified llvm byte code:
+
+; ModuleID = 'llvm_clang_demo.ll'
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+define i32 @foo(i32 %a, i32 %b) nounwind uwtable readnone {
+  %1 = add nsw i32 %b, %a
+  ret i32 %1
+}
+ 
 */
 
 int foo(int a, int b)