Add label support for kubectl describe

Add -l option to kubectl describe command, allow it return
multiple results filtered by label selector.

docs/man/man1/kubectl-describe.1

@@ -25,6 +25,10 @@ given resource.
 \fB\-h\fP, \fB\-\-help\fP=false
     help for describe
 
+.PP
+\fB\-l\fP, \fB\-\-selector\fP=""
+    Selector (label query) to filter on
+
 
 .SH OPTIONS INHERITED FROM PARENT COMMANDS
 .PP
@@ -135,6 +139,9 @@ $ kubectl describe nodes kubernetes\-minion\-emt8.c.myproject.internal
 // Describe a pod
 $ kubectl describe pods/nginx
 
+// Describe pods by label name=myLabel
+$ kubectl describe po \-l name=myLabel
+
 .fi
 .RE