update configuration and documentation

.env.example

@@ -0,0 +1,11 @@
+DB_URL=jdbc:postgresql://<host>:<port>/<db>
+DB_USER=<db_user>
+DB_PASSWORD=<db_password>
+
+WISHLISTS_USERNAME=<login_1>
+WISHLISTS_PASSWORD=<password_1>
+GIFTS_USERNAME=<login_2>
+GIFTS_PASSWORD=<password_2>
+RESERVATION_USERNAME=<login_3>
+RESERVATION_PASSWORD=<password_3>
+RESERVATION_OWNER=<login_owner>