Update readme

Author: ecarriou

src/systems/README.md

@@ -3,7 +3,8 @@
 System Runtime has got a customizable system. You can update all its components, models or behaviors to follow your needs. To do so:
 
 * open a version of [System Designer](https://designfirst.io/systemdesigner/),
-* edit the system you want,
+* import the system you want,
+* edit the system,
 * export it,
 * save it in the same place and
 * run `npm run build`.