docs: Updating minimum Kubernetes version

Also minor update to the eventing  docs for watching logs

Fixes #30

Author: kameshsampath

documentation/modules/ROOT/pages/05eventing/eventing-src-sub.adoc

@@ -323,6 +323,8 @@ kubectl apply -n knativetutorial -f service.yaml
 oc apply -n knativetutorial -f service.yaml 
 ----
 
+You can xref:05eventing/eventing.adoc#eventing-watch-logs[watch logs] to see the cron job source sending an event every 1 minute.
+
 [#eventing-cleanup]
 == Cleanup
 

documentation/modules/ROOT/pages/05eventing/eventing-src-svc.adoc

@@ -178,7 +178,7 @@ kubectl apply -n knativetutorial -f service.yaml
 oc apply -n knativetutorial -f service.yaml 
 ----
 
-You can xref:05eventing/eventing.adoc#eventing-watch-logs[watch logs] to see the cron job source sending event every 1 minute.
+You can xref:05eventing/eventing.adoc#eventing-watch-logs[watch logs] to see the cron job source sending an event every 1 minute.
 
 [#eventing-see-what-you-have-deployed]
 === See what you have deployed

documentation/modules/ROOT/pages/_partials/prereq-cli.adoc

@@ -19,7 +19,7 @@ eval $(minishift docker-env) && eval $(minishift oc-env)
 
 [source,bash]
 ----
-# kubernetes v1.11+
+# kubernetes v1.12+
 kubectl version
 ----
 

documentation/modules/ROOT/pages/setup.adoc

@@ -106,13 +106,15 @@ Before installing Knative and its components, we need to add few startup config
 [source,bash,subs="+macros,+attributes"]
 ----
 minikube start -p knative --memory=8192 --cpus=4 \#<1> 
-  --vm-driver=hyperkit \#<2>
+  --kubernetes-version=v1.12.0 \#<2> 
+  --vm-driver=hyperkit \#<3>  
   --disk-size=50g \
   --extra-config=apiserver.enable-admission-plugins="LimitRanger,NamespaceExists,NamespaceLifecycle,ResourceQuota,ServiceAccount,DefaultStorageClass,MutatingAdmissionWebhook"
 ----
 
 <1> Starting a profile named **knative**
-<2> If you are on linux then use `--vm-driver=kvm2`
+<2> Minimum kubernetes version needs to be >= 1.12.0, refer to issue https://github.com/knative/serving/issues/3067 for more details.
+<3> If you are on linux then use `--vm-driver=kvm2`
 
 [#install-knative-istio]
 ==== Install Istio