Tempo: Add note about how to send traces from grafana to devenv readme (grafana#79893)

Author: aocenas

devenv/docker/blocks/tempo/README.md

@@ -4,3 +4,10 @@ This devenv docker-compose.yaml will allow you to;
 - upload/download trace JSON files
 - view service graphs
 - search traces via Loki
+
+To send traces from grafana use this configuration;
+```
+[tracing.opentelemetry.otlp]
+# otlp destination (ex localhost:4317)
+address = localhost:4317
+```