Add note about how to put binaries in project root

doc/articles/vendor-binaries.md

@@ -111,3 +111,5 @@ An example of the former looks like this:
 Running `composer install` for this `composer.json` will result in
 all of the vendor binaries being installed in `scripts/` instead of
 `vendor/bin/`.
+
+You can set `bin-dir` to `./` to put binaries in your project root.