[www] fix wrong statement regarding alloca placement

Author: isuckatcs

www/codegen.html

@@ -387,11 +387,13 @@ <h2>Allocating Stack Variables</h2>
                     block.
                 </p>
                 <p>
-                    The problem with inserting at the end of the block is that
-                    the variables always appear after they are used, which is an
-                    error. A different approach might be to always insert before
-                    the first instruction, but in that case, it's always the
-                    latest variable appearing first, so the order is reversed.
+                    Certain optimization passes only work if all of the
+                    variables are allocated in the entry block of the function,
+                    so allocating them into the most recent block is missing out
+                    on a better optimized code. A different approach might be to
+                    always insert before the first instruction, but in that
+                    case, it's always the latest variable appearing first, so
+                    the order is reversed.
                 </p>
                 <p>
                     The idea is to insert a placeholder instruction at the