docs: make CONTRIBUTING instructions work & fix example envs (#152)

backend/.env.example

@@ -1,6 +1,8 @@
 APP_ENV=production
 PUBLIC_APP_URL=http://localhost
+# /!\ If PUBLIC_APP_URL is not a localhost address, it must be HTTPS
 DB_PROVIDER=sqlite
+# MAXMIND_LICENSE_KEY=fixme # needed for IP geolocation in the audit log
 SQLITE_DB_PATH=data/pocket-id.db
 POSTGRES_CONNECTION_STRING=postgresql://postgres:postgres@localhost:5432/pocket-id
 UPLOAD_PATH=data/uploads

backend/internal/bootstrap/bootstrap.go

@@ -6,9 +6,10 @@ import (
 )
 
 func Bootstrap() {
+	initApplicationImages()
+
 	db := newDatabase()
 	appConfigService := service.NewAppConfigService(db)
 
-	initApplicationImages()
 	initRouter(db, appConfigService)
 }