update docs for genrule tool_files prop

According to go/roboleaf-busy-beavers-sandboxing, this field should just take in any data files needed by the tool. The existing description makes it sound like this property should only contain a single file that will be used as the tool itself.

Change-Id: I3ef3b8ceb52f7a7e6de9e0a897d5cc05c9c2d336
diff --git a/genrule/genrule.go b/genrule/genrule.go
index aa4295d..8e3f278 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -140,7 +140,7 @@
 	// prebuilts or scripts that do not need a module to build them.
 	Tools []string
 
-	// Local file that is used as the tool
+	// Local files that are used by the tool
 	Tool_files []string `android:"path"`
 
 	// List of directories to export generated headers from
@@ -403,7 +403,6 @@
 	}
 
 	addLabelsForInputs := func(propName string, include, exclude []string) android.Paths {
-
 		includeDirInPaths := ctx.DeviceConfig().BuildBrokenInputDir(g.Name())
 		var srcFiles android.Paths
 		for _, in := range include {