doc: improve component override precedence priority explanation

Feedback by @dbyrns.

birdhouse/env.local.example

@@ -52,9 +52,19 @@ export POSTGRES_MAGPIE_PASSWORD=postgres-qwerty
 # * Assemble different combinations of components/functionalities by including
 #   only the config/docker-compose fragment necessary.
 #
-# Last dir/docker-compose fragment in the list have highest override precedence.
-# Ex: last docker-compose volume mount to same destination win over the
-# previous docker-compose volume mount.
+# Last dir/component in the EXTRA_CONF_DIRS list have highest override
+# precedence, example:
+#
+#   * Last docker-compose volume mount to same destination win over the
+#     previous docker-compose volume mount.
+#
+#   * Last default.env can change the values of all previous default.env.
+#
+#   * Last pre/post docker-compose-up script can potentially undo actions
+#     from previous scripts.
+#
+# Suggested to keep the private-config-repo last in the list to be able to
+# override anything.
 #
 # Format: space separated list of dirs
 #