add .env.local.example

.env.local.example

+BACKEND_URL=http://localhost:8080
+# You can use the builtin webpack proxy during development which will connect you to BACKEND_URL
+REACT_APP_BACKEND_URL=http://127.0.0.1:8080
+
+REACT_APP_CHECK_STATUS_INTERVAL=0
+REACT_APP_TRACING_ENABLED=false
+REACT_APP_SENTRY_DSN=
+REACT_APP_TRACE_SAMPLE_RATE=1
+REACT_APP_RELEASE=local
+REACT_APP_ENVIRONMENT=local
+REACT_APP_TRACING_ORIGINS=*
+
+# Fill in when Enabling OAUTH2
+REACT_APP_OAUTH2_ENABLED=False
+REACT_APP_OAUTH2_CLIENT_ID=
+REACT_APP_OAUTH2_OPENID_CONNECT_URL=
+REACT_APP_OAUTH2_SCOPE=
+
+# Needed because some libs misbehave
+GENERATE_SOURCEMAP=false
+FAST_REFRESH=false