Add basic scenario description

src/scenarios/cache-stampede/README.md

@@ -1,4 +1,19 @@
-```metrics
-system.fn_duration_ms{service=api}
-system.fn_duration_ms{service=db}
-```
+# Cache Stampede
+
+In this scenario, we look into cache stampede caused by cache flush.
+
+## Setup
+
+The system consist of an API server, a cache, and a database.
+
+Database query is slow (~20ms), and cache query is fast (~1ms).
+
+
+## Useful metrics
+
+- [API latency](lab:metrics?q=system.fn_duration_ms{service=api})
+- [DB latency](lab:metrics?q=system.fn_duration_ms{service=db})
+- [DB load](lab:metrics?q=system.node_load{service=db})
+- [Cache latency](lab:metrics?q=system.fn_duration_ms{service=cache})
+- [Cache hits](lab:metrics?q=services.cache.hit)
+- [Cache misses](lab:metrics?q=services.cache.miss)