Write intro to robust javascript interactivity

Author: RoyalIcing

lib/components_guide_web/templates/robust_javascript_interactivity/intro.html.md

@@ -1,2 +1,11 @@
 # What goes wrong with interactive JavaScript apps?
 
+- The user gets confused:
+  - The layout looks broken on their device.
+  - The content sounds broken on their device.
+  - They can’t find what they are looking for.
+  - They can’t successfully interact with widgets on the page.
+  - They don’t understand the information that is being provided.
+- The network fails.
+- A browser doesn’t support a feature being used.
+- Browser extensions corrupt the page.