To add specific content below the products grid on a specefic collection page :

1- On template editor find “Sections”

2- Click on “Add a new section” and a name to the section you want to beshown below grid

3- Enter what ever you desire, like simple HTML, in new created section

4- Save the new section and find “collection.liquid” in “Templates”

5- Add following condition to the end of the file :

Copy to Clipboard

6- Save and go! 😉