(#353) Add an empty, commented .sync.yml

Fixes #353.

moduleroot_init/.sync.yml.erb

+# This file can be used to customize the files managed by PDK.
+#
+# See https://github.com/puppetlabs/pdk-templates/blob/main/README.md
+# for more information.
+#
+# See https://github.com/puppetlabs/pdk-templates/blob/main/config_defaults.yml
+# for the default values.
+--- {}