Update docs to add note about disabling startup timeout

Author: JoelSpeed

docs/book/src/tasks/healthcheck.md

@@ -38,7 +38,9 @@ spec:
   # (Optional) maxUnhealthy prevents further remediation if the cluster is already partially unhealthy
   maxUnhealthy: 40%
   # (Optional) nodeStartupTimeout determines how long a MachineHealthCheck should wait for
-  # a Node to join the cluster, before considering a Machine unhealthy
+  # a Node to join the cluster, before considering a Machine unhealthy.
+  # Defaults to 10 minutes if not specified.
+  # Set to 0 to disable this check.
   nodeStartupTimeout: 10m
   # selector is used to determine which Machines should be health checked
   selector: