Add Health checks section to CLI docs (#876)

src/pages/get-started/cli.mdx

@@ -427,6 +427,26 @@ Peers count: 2/3 Connected
     The peer with IP `100.119.85.4` wasn't returned because it was not connected
 </Note>
 
+#### Health checks
+
+Use `netbird status --check` to run a health probe from a script or container orchestrator. These probes do not display the normal status report. A successful probe produces no output and exits with code `0`; a failed probe exits with code `1`.
+
+- `live`: succeeds when the daemon responds to the status request.
+- `ready`: succeeds when the daemon status is `Idle`, `Connecting`, or `Connected`. Authentication-required states (`NeedsLogin`, `LoginFailed`, and `SessionExpired`) and unexpected states fail the check.
+- `startup`: succeeds when management and signal are connected and, if any NetBird relays are configured, at least one relay is available.
+
+For example, the following loop makes each probe result visible:
+
+```shell
+for check in live ready startup; do
+  if netbird status --check "$check"; then
+    echo "$check: PASS"
+  else
+    echo "$check: FAIL ($?)"
+  fi
+done
+```
+
 ### ssh
 Command to connect via SSH to a remote peer in your NetBird network. The `ssh` command has several subcommands for different operations.