Add instructions to get API key

Author: notsniped

README.md

@@ -10,6 +10,9 @@ SkyblockPy works by communicating with the Hypixel API endpoints by using your *
 
 If no errors are returned by the API endpoint (status code 200 is returned), then the API output is returned as a `dict`.
 
+### Obtaining an API key
+Go to the Hypixel Minecraft Java server and use `/api` command.
+
 ### I found a bug/I want to add a missing feature!
 Just make a new issue [here](https://github.com/PyBotDevs/skyblockpy/issues/new) and describe the bug/feature.