Updated README to mention env files (#5)

README.md

@@ -4,6 +4,16 @@ Interactive editor for fabrix framework
 
 ## Setup
 
+Before setup, you have to set `VITE_GRAPHQL_ENDPOINT_URL` in your environment.
+
+You can use an example GQL server by copy-pasting the configuration below to `.env` in your local.
+
+```
+VITE_GRAPHQL_ENDPOINT_URL=https://starwars-9teh3dbd8w.erp.dev/query`
+```
+
+Then, spin up an editor app.
+
 ```
 pnpm install
 ```