docs: add installation description for Vue 3.x and Vue 2.x

bastidest · bastidest · commit f938c1b71074 · 2022-07-28T13:59:28.000+02:00
diff --git a/README.md b/README.md
@@ -8,7 +8,11 @@
 
 Install the plugin with npm:
 ```shell
+# Vue 3.x
 npm install --save vue-step-progress
+
+# Vue 2.x
+npm install --save vue-step-progress@0
 ```
 
 ## Usage
