Update README.md and improve docs.

Author: wi1dcard

README.md

@@ -3,7 +3,9 @@
 ![](https://img.shields.io/github/workflow/status/darwinia-network/node-liveness-probe/Production)
 ![](https://img.shields.io/github/v/release/darwinia-network/node-liveness-probe)
 
-The node liveness probe is a sidecar container that exposes an HTTP `/healthz` endpoint, which serves as kubelet's livenessProbe hook to monitor health of a Darwinia node.
+The node liveness probe is a sidecar container that exposes an HTTP `/healthz` endpoint, which calls several RPC methods via a WebSocket connection to check and serves as kubelet's livenessProbe hook to monitor health of a Darwinia node.
+
+It also experimentally provides a readiness probe endpoint `/readiness`, which reports if the node is ready to handle RPC requests by determining if the syncing progress is done.
 
 ## Releases
 
@@ -28,15 +30,18 @@ spec:
  ports:
  - name: healthz
  containerPort: 49944
- # The probe
- readinessProbe: &probe
+ # The liveness probe
+ livenessProbe:
  httpGet:
  path: /healthz
  port: healthz
- timeoutSeconds: 3
- livenessProbe:
- <<: *probe
  initialDelaySeconds: 60
+ timeoutSeconds: 3
+ # The experimental readiness probe
+ readinessProbe:
+ httpGet:
+ path: /readiness
+ port: healthz
  # ...
 
  # The liveness probe sidecar container
@@ -49,12 +54,20 @@ spec:
 
 Notice that the actual `livenessProbe` field is set on the node container. This way, Kubernetes restarts darwinia node instead of node-liveness-probe when the probe fails. The liveness probe sidecar container only provides the HTTP endpoint for the probe and does not contain livenessProbe section by itself.
 
+It is recommended to increase the option `--timeout` and Pod spec `.containers.*.livenessProbe.timeoutSeconds` a bit (e.g. 3 seconds), if you have a heavy load on your node, since the probe process involves multiple RPC calls.
+
+## Configuration
+
 To get the full list of configurable options, please use `--help`:
 
 ```bash
 docker run --rm -it quay.io/darwinia-network/node-liveness-probe:VERSION --help
 ```
 
+## Compatibility
+
+The node liveness probe should be compatible with nodes of other Substrate-based chains, such as Polkadot and Kusama, although that hasn't been well tested. Please consider submitting an issue if you're experiencing any problem with these nodes to help us improve the compatibilities.
+
 ## Special Thanks
 
 - <https://github.com/kubernetes-csi/livenessprobe>