Move English documentation to folder en_US

doc/en_US/postgresql-configuration.markdown

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+Postgresql configuration
+========================
+
+By default, Kanboard use Sqlite to store its data but it's also possible to use Postgresql.
+
+Requirements
+------------
+
+- Postgresql >= 9.3
+- 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
+
+The file `config.php` should contain those values:
+
+```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');
+```
+
+Note: You can also rename the template file `config.default.php` to `config.php`.
+
+### Importing SQL dump (alternative method)
+
+For the first time, Kanboard will run one by one each database migration and this process can take some time according to your configuration.
+
+To avoid any issues or potential timeouts, you can initialize the database directly by importing the SQL schema:
+
+```bash
+psql -U postgres my_database < app/Schema/Sql/postgres.sql
+```
+
+The file `app/Schema/Sql/postgres.sql` is a SQL dump that represents the last version of the database.