Link usage of unpublish workflow if users want to teardown PR preview site

[tlylt]

As discussed in #1 (review), will be good to include a way for users to auto teardown their PR preview site if they want.
I came up with a solution here but as the reusable workflows might take more time for testing etc, I will open this issue to keep track of the todo

• link to the reusable workflow when ready, to show users how to setup a action file to auto teardown PR preview site