Rename conf dir > custom.sample (#1522)

* Explain app.ini purpose

conf/app.ini → custom.sample/app.ini

@@ -1,3 +1,7 @@
+; This file lists the default values used by Gitea
+; Copy required sections to your own app.ini (default is custom/conf/app.ini)
+; and modify as needed.
+
 ; App name that shows on every page title
 APP_NAME = Gitea: Git with a cup of tea
 ; Change it if you run locally