add comma

Author: PureWhiteWu

doc/asm.html

@@ -603,7 +603,7 @@ <h3 id="x86">32-bit Intel 386</h3>
 with a pointer to the <code>g</code> pointer, and the <code>g</code> struct
 contains the <code>m</code> pointer.
 There's another special header containing the offsets for each
-element of <code>g</code> called <code>go_asm.h</code>.
+element of <code>g</code>, called <code>go_asm.h</code>.
 The sequence to load <code>g</code> and <code>m</code> using <code>CX</code> looks like this:
 </p>