Add details about database url

Author: lovasoa

configuration.md

@@ -9,7 +9,7 @@ Here are the available configuration options and their default values:
 | variable                                      | default                                                     | description                                                                                                                                                                                                                                            |
 | --------------------------------------------- | ----------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
 | `listen_on`                                   | 0.0.0.0:8080                                                | Interface and port on which the web server should listen                                                                                                                                                                                               |
-| `database_url`                                | sqlite://sqlpage.db?mode=rwc                                | Database connection URL                                                                                                                                                                                                                                |
+| `database_url`                                | sqlite://sqlpage.db?mode=rwc                                | Database connection URL, in the form `dbname://user:password@host:port/dbname`. Special characters in user and password should be [percent-encoded](https://developer.mozilla.org/en-US/docs/Glossary/percent-encoding). |
 | `port`                                        | 8080                                                        | Like listen_on, but specifies only the port.                                                                                                                                                                                                           |
 | `max_database_pool_connections`               | PostgreSQL: 50<BR>  MySql: 75<BR> SQLite: 16<BR> MSSQL: 100 | How many simultaneous database connections to open at most                                                                                                                                                                                             |
 | `database_connection_idle_timeout_seconds`    | SQLite: None<BR> All other: 30 minutes                      | Automatically close database connections after this period of inactivity                                                                                                                                                                               |