Add Postgresql support

docs/postgresql-configuration.markdown

@@ -0,0 +1,38 @@
+Postgresql configuration
+========================
+
+By default, Kanboard use Sqlite to store its data but it's also possible to use Postgresql.
+
+Requirements
+------------
+
+- A Postgresql server already installed and configured
+- The PHP extension `pdo_pgsql` installed (Debian/Ubuntu: `apt-get install php5-pgsql`)
+
+Configuration
+-------------
+
+### Create an empty database with the command `pgsql`:
+
+```sql
+CREATE DATABASE kanboard;
+```
+
+### Create a config file
+
+Inside our config file write those lines:
+
+```php
+<?php
+
+// We choose to use Postgresql instead of Sqlite
+define('DB_DRIVER', 'postgres');
+
+// Mysql parameters
+define('DB_USERNAME', 'REPLACE_ME');
+define('DB_PASSWORD', 'REPLACE_ME');
+define('DB_HOSTNAME', 'REPLACE_ME');
+define('DB_NAME', 'kanboard');
+```
+
+Now, you are ready to use Postgresql.