Add note on config file usage

Author: ohsayan

docs/system/1.configuration.md

@@ -37,6 +37,10 @@ endpoints:
     port: 2003
 ```
 
+:::info Starting the server with a configuration file
+To start the server with a configuration file, simply run `skyd --config <path to config>.yaml`
+:::
+
 Here's an explanation of all the keys:
 - `system`:
   - `mode`: set to either `dev` / `prod` mode. `prod` mode will generally make some things stricters (such as background services)