add missing link

Author: MrYamous

bundles/best_practices.rst

@@ -566,3 +566,4 @@ Learn more
 .. _`valid license identifier`: https://spdx.org/licenses/
 .. _`GitHub Actions`: https://docs.github.com/en/free-pro-team@latest/actions
 .. _`Travis CI`: https://docs.travis-ci.com/
+.. _`Symfony 4.4 bundle documentation`: https://symfony.com/doc/4.4/bundles.html#bundle-directory-structure