Add configuration guide

README.md

@@ -66,3 +66,8 @@ Add a new domain and user.
 ```
 
 Enjoy!
+
+More info
+---------
+
+See [documentation](doc/README.md)

doc/README.md

@@ -0,0 +1,5 @@
+Documentation
+=============
+
+- [Configuration](configuration.md)
+- [Migrating from mailfull](migrating_from_mailfull.md)

doc/configuration.md

@@ -0,0 +1,12 @@
+Configuration
+=============
+
+`.mailfull/config`
+
+| key | type | default | required | description |
+|:----|:-----|:--------|:---------|:------------|
+| dir_database | string | `"./etc"` | no | A relative path from repository dir (or a absolute path) |
+| dir_maildata | string | `"./domains"` | no | A relative path from repository dir (or a absolute path) |
+| username | string | The username who executed `mailfull init` | **yes** | It used for setting owner of database files and maildata files. |
+| cmd_postalias | string | `"postalias"` | no | Command name or path |
+| cmd_postmap | string | `"postmap"` | no | Command name or path |