docs(pillar.example): improve TOFS comment to explain the default path [skip ci]

* As used in the `nginx-formula`:
  - 17291a0ae2/pillar.example (L340-L341)

pillar.example

@@ -32,6 +32,8 @@ template:
       - os_family
     # All aspects of path/file resolution are customisable using the options below.
     # This is unnecessary in most cases; there are sensible defaults.
+    # Default path: salt://{{ path_prefix }}/{{ dirs.files }}/{{ dirs.default }}
+    #         I.e.: salt://template/files/default
     # path_prefix: template_alt
     # dirs:
     #   files: files_alt