How to inject HTML code block into the theme during app installation?

[mrkarim]

Hello Developers, 

I am trying to build an app where during my app installation I will add some HTML code blocks to /collection/ page. 

I am new to shopify app development. So I am a bit confused about how to do that. Here is an example of what I am expecting.

add the following code block to the /collection/ page

<div>Some information</div>