chore: add docs for config file (#4432)

config/config.md

@@ -269,15 +269,15 @@
 | `procedure.retry_delay` | String | `500ms` | Initial retry delay of procedures, increases exponentially |
 | `procedure.max_metadata_value_size` | String | `1500KiB` | Auto split large value<br/>GreptimeDB procedure uses etcd as the default metadata storage backend.<br/>The etcd the maximum size of any request is 1.5 MiB<br/>1500KiB = 1536KiB (1.5MiB) - 36KiB (reserved size of key)<br/>Comments out the `max_metadata_value_size`, for don't split large value (no limit). |
 | `failure_detector` | -- | -- | -- |
-| `failure_detector.threshold` | Float | `8.0` | -- |
-| `failure_detector.min_std_deviation` | String | `100ms` | -- |
-| `failure_detector.acceptable_heartbeat_pause` | String | `10000ms` | -- |
-| `failure_detector.first_heartbeat_estimate` | String | `1000ms` | -- |
+| `failure_detector.threshold` | Float | `8.0` | The threshold value used by the failure detector to determine failure conditions. |
+| `failure_detector.min_std_deviation` | String | `100ms` | The minimum standard deviation of the heartbeat intervals, used to calculate acceptable variations. |
+| `failure_detector.acceptable_heartbeat_pause` | String | `10000ms` | The acceptable pause duration between heartbeats, used to determine if a heartbeat interval is acceptable. |
+| `failure_detector.first_heartbeat_estimate` | String | `1000ms` | The initial estimate of the heartbeat interval used by the failure detector. |
 | `datanode` | -- | -- | Datanode options. |
 | `datanode.client` | -- | -- | Datanode client options. |
-| `datanode.client.timeout` | String | `10s` | -- |
-| `datanode.client.connect_timeout` | String | `10s` | -- |
-| `datanode.client.tcp_nodelay` | Bool | `true` | -- |
+| `datanode.client.timeout` | String | `10s` | Operation timeout. |
+| `datanode.client.connect_timeout` | String | `10s` | Connect server timeout. |
+| `datanode.client.tcp_nodelay` | Bool | `true` | `TCP_NODELAY` option for accepted connections. |
 | `wal` | -- | -- | -- |
 | `wal.provider` | String | `raft_engine` | -- |
 | `wal.broker_endpoints` | Array | -- | The broker endpoints of the Kafka cluster. |

config/metasrv.example.toml

@@ -58,17 +58,32 @@ max_metadata_value_size = "1500KiB"
 
 # Failure detectors options.
 [failure_detector]
+
+## The threshold value used by the failure detector to determine failure conditions.
 threshold = 8.0
+
+## The minimum standard deviation of the heartbeat intervals, used to calculate acceptable variations.
 min_std_deviation = "100ms"
+
+## The acceptable pause duration between heartbeats, used to determine if a heartbeat interval is acceptable.
 acceptable_heartbeat_pause = "10000ms"
+
+## The initial estimate of the heartbeat interval used by the failure detector.
 first_heartbeat_estimate = "1000ms"
 
 ## Datanode options.
 [datanode]
+
 ## Datanode client options.
 [datanode.client]
+
+## Operation timeout.
 timeout = "10s"
+
+## Connect server timeout.
 connect_timeout = "10s"
+
+## `TCP_NODELAY` option for accepted connections.
 tcp_nodelay = true
 
 [wal]