Add admin user instructions

README.md

@@ -35,6 +35,10 @@ config :pleroma, :instance,
   registrations_open: true,
   federating: true
 ```
+Add an instance admin like this:
+```
+docker exec pleroma /opt/pleroma/bin/pleroma_ctl user new joeuser joeuser@sld.tld --admin -y
+```
 
 The postgres database files are located in `./volumes/pleroma-db/pgdata`. You can also insert postgres startup scripts inside `./volumes/pleroma-db/pginit`