Adding detail of how to check the OS/kernel version

Insert the command to check the version of OS and kernel
in order to get more detail in ISSUE_TEMPLATE.

Signed-off-by: Nguyen Hai Truong <truongnh@vn.fujitsu.com>

.github/ISSUE_TEMPLATE.md

@@ -2,7 +2,11 @@
 
 Output of `helm version`:
 
-Output of `kubectl version`:
+Output of `kubectl version`:  
+
+Output of `cat /etc/os-release`:  
+
+Output of `uname -r`:
 
 Cloud Provider/Platform (AKS, GKE, Minikube etc.):