runtime: add doc to remind adopting changes to reflectlite

Updates #34486

Change-Id: Iec9a5d120013aaa287eccf2999b3f2b831be070e
Reviewed-on: https://go-review.googlesource.com/c/go/+/197558
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/type.go

@@ -14,6 +14,7 @@ import "unsafe"
 //	cmd/compile/internal/gc/reflect.go
 //	cmd/link/internal/ld/decodesym.go
 //	reflect/type.go
+//      internal/reflectlite/type.go
 type tflag uint8
 
 const (
@@ -26,6 +27,7 @@ const (
 // Needs to be in sync with ../cmd/link/internal/ld/decodesym.go:/^func.commonsize,
 // ../cmd/compile/internal/gc/reflect.go:/^func.dcommontype and
 // ../reflect/type.go:/^type.rtype.
+// ../internal/reflectlite/type.go:/^type.rtype.
 type _type struct {
 	size       uintptr
 	ptrdata    uintptr // size of memory prefix holding all pointers