Document constraints of dynamic config install

Non-changeable fields can cause issues if not defined in the
configuration file. This isn't immediately obvious by reading the docs
so document it explicitly.

Signed-off-by: Juan-Luis de Sousa-Valadas Castaño <jvaladas@mirantis.com>

docs/dynamic-configuration.md

@@ -51,6 +51,11 @@ As with any Kubernetes cluster there are certain things that just cannot be chan
 - `network.serviceCIDR`
 - `network.provider`
 
+During the manual installation of control plane nodes with `k0s install`, all these
+non-changeable options must be defined in the configuration file. This is necessary
+because these fields can be used before the dynamic configuration reconciler is
+initialized. Both k0sctl and k0smotron handle this without user intervention.
+
 ## Configuration status
 
 The dynamic configuration reconciler operator will write status events for all the changes it detects. To see all dynamic config related events, use: