Link to documentation about variables in include statements

As requested in aosp/1962181

Fixes: 217248902
Test: Presubmits
Change-Id: Ib0f99a4b86999782bfcf3ccf89375a929cf5127f
diff --git a/mk2rbc/node.go b/mk2rbc/node.go
index 61aaf91..2fa6a85 100644
--- a/mk2rbc/node.go
+++ b/mk2rbc/node.go
@@ -101,7 +101,7 @@
 func (i inheritedDynamicModule) emitSelect(gctx *generationContext) {
 	if i.needsWarning {
 		gctx.newLine()
-		gctx.writef("%s.mkwarning(%q, %q)", baseName, i.location, "Including a path with a non-constant prefix, please convert this to a simple literal to generate cleaner starlark.")
+		gctx.writef("%s.mkwarning(%q, %q)", baseName, i.location, "Including a path with a non-constant prefix, please convert this to a simple literal to generate cleaner starlark. See https://source.android.com/setup/build/bazel/product_config/issues/includes for details.")
 	}
 	gctx.newLine()
 	gctx.writef("_entry = {")