add metrics example to readme

README.md

@@ -21,3 +21,41 @@ make build
 ```
 curl http://localhost:1640
 ```
+
+## Metrics
+
+* `swarm_stamp_batch_available_bytes` (gauge)
+* `swarm_stamp_batch_capacity_bytes` (gauge)
+* `swarm_stamp_batch_depth` (gauge)
+* `swarm_stamp_batch_ttl` (gauge)
+* `swarm_stamp_batch_usage_percentage` (gauge)
+* `swarm_stamp_batch_utilization` (gauge)
+
+Example:
+
+```
+# HELP swarm_stamp_batch_available_bytes Stamp batch available capacity in bytes.
+# TYPE swarm_stamp_batch_available_bytes gauge
+swarm_stamp_batch_available_bytes{batchID="394c6927473b0441b7e0a2bfd94494c4de5b3a3a1515e9689f03d4aac32d7913",label="blobs2"} 1.62940321792e+11
+swarm_stamp_batch_available_bytes{batchID="f384b94640b64d04d738eec79fc82a18dde7bc9677b0be28836dd63957b72e46",label="blobs"} 4.294967296e+09
+# HELP swarm_stamp_batch_capacity_bytes Stamp batch total capacity in bytes.
+# TYPE swarm_stamp_batch_capacity_bytes gauge
+swarm_stamp_batch_capacity_bytes{batchID="394c6927473b0441b7e0a2bfd94494c4de5b3a3a1515e9689f03d4aac32d7913",label="blobs2"} 2.74877906944e+11
+swarm_stamp_batch_capacity_bytes{batchID="f384b94640b64d04d738eec79fc82a18dde7bc9677b0be28836dd63957b72e46",label="blobs"} 4.294967296e+09
+# HELP swarm_stamp_batch_depth Stamp batch depth.
+# TYPE swarm_stamp_batch_depth gauge
+swarm_stamp_batch_depth{batchID="394c6927473b0441b7e0a2bfd94494c4de5b3a3a1515e9689f03d4aac32d7913",label="blobs2"} 26
+swarm_stamp_batch_depth{batchID="f384b94640b64d04d738eec79fc82a18dde7bc9677b0be28836dd63957b72e46",label="blobs"} 20
+# HELP swarm_stamp_batch_ttl Stamp batch TTL.
+# TYPE swarm_stamp_batch_ttl gauge
+swarm_stamp_batch_ttl{batchID="394c6927473b0441b7e0a2bfd94494c4de5b3a3a1515e9689f03d4aac32d7913",label="blobs2"} 2.990461e+06
+swarm_stamp_batch_ttl{batchID="f384b94640b64d04d738eec79fc82a18dde7bc9677b0be28836dd63957b72e46",label="blobs"} 133323
+# HELP swarm_stamp_batch_usage_percentage Stamp batch usage percentage.
+# TYPE swarm_stamp_batch_usage_percentage gauge
+swarm_stamp_batch_usage_percentage{batchID="394c6927473b0441b7e0a2bfd94494c4de5b3a3a1515e9689f03d4aac32d7913",label="blobs2"} 0.5927734375
+swarm_stamp_batch_usage_percentage{batchID="f384b94640b64d04d738eec79fc82a18dde7bc9677b0be28836dd63957b72e46",label="blobs"} 1
+# HELP swarm_stamp_batch_utilization Stamp batch utilization.
+# TYPE swarm_stamp_batch_utilization gauge
+swarm_stamp_batch_utilization{batchID="394c6927473b0441b7e0a2bfd94494c4de5b3a3a1515e9689f03d4aac32d7913",label="blobs2"} 607
+swarm_stamp_batch_utilization{batchID="f384b94640b64d04d738eec79fc82a18dde7bc9677b0be28836dd63957b72e46",label="blobs"} 16
+```