docs: Add link to Killercoda interactive course (argoproj#12306)

Signed-off-by: Yuan (Terry) Tang <terrytangyuan@gmail.com>
Signed-off-by: 刘达 <liuda1@kingsoft.com>

README.md

@@ -39,7 +39,10 @@ Argo is a [Cloud Native Computing Foundation (CNCF)](https://cncf.io/) graduated
 
 ## Try Argo Workflows
 
-[Access the demo environment](https://workflows.apps.argoproj.io/workflows/argo) (login using Github)
+You can try Argo Workflows via one of the following:
+
+1. [Interactive Training Material](https://killercoda.com/argoproj/course/argo-workflows/)
+1. [Access the demo environment](https://workflows.apps.argoproj.io/workflows/argo)
 
 ![Screenshot](docs/assets/screenshot.png)