Add more documentation

Override-default-dovecot-configuration.md

@@ -1,3 +1,25 @@
 The Dovecot default configuration can easily be overridden providing a `config/dovecot.cf` file.
 This file can also be used to specify additional configurations.
 [Dovecot documentation](http://wiki.dovecot.org/FrontPage) remains the best place to find configuration options.
+
+# Debugging
+
+To debug your dovecot configuration you can use this command:
+
+```sh
+./setup.sh debug login doveconf | grep <some-keyword>
+```
+
+[setup.sh](https://github.com/tomav/docker-mailserver/blob/master/setup.sh) is included in the `docker-mailserver` repository.
+
+or
+
+```sh
+docker exec -ti <your-container-name> doveconf | grep <some-keyword>
+```
+
+The  `config/dovecot.cf` is copied to `/etc/dovecot/local.conf`. To check this file run:
+
+```sh
+docker exec -ti <your-container-name> cat /etc/dovecot/local.conf
+```