Add markdown CI (#5380)

docs/netcheck.md

@@ -1,5 +1,4 @@
-Network Checker Application
-===========================
+# Network Checker Application
 
 With the ``deploy_netchecker`` var enabled (defaults to false), Kubespray deploys a
 Network Checker Application from the 3rd side `l23network/k8s-netchecker` docker
@@ -14,14 +13,17 @@ logs.
 
 To get the most recent and cluster-wide network connectivity report, run from
 any of the cluster nodes:
-```
+
+```ShellSession
 curl http://localhost:31081/api/v1/connectivity_check
 ```
+
 Note that Kubespray does not invoke the check but only deploys the application, if
 requested.
 
 There are related application specific variables:
-```
+
+```yml
 netchecker_port: 31081
 agent_report_interval: 15
 netcheck_namespace: default
@@ -33,7 +35,7 @@ combination of the ``netcheck_namespace.dns_domain`` vars, for example the
 to the non default namespace, make sure as well to adjust the ``searchdomains`` var
 so the resulting search domain records to contain that namespace, like:
 
-```
+```yml
 search: foospace.cluster.local default.cluster.local ...
 nameserver: ...
 ```