[x86 setup] MAINTAINERS: document x86 setup code git tree

Document the existence of a published git tree for the x86 setup code.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

MAINTAINERS

@@ -1740,6 +1740,7 @@ S:	Maintained
 i386 SETUP CODE / CPU ERRATA WORKAROUNDS
 P:	H. Peter Anvin
 M:	hpa@zytor.com
+T:	git.kernel.org:/pub/scm/linux/kernel/git/hpa/linux-2.6-x86setup.git
 S:	Maintained
 
 IA64 (Itanium) PLATFORM