Add description of Power-Up

We need to add the description of this Power-Up.

GitLab	GitHub	BitBucket	Example of one with just text

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The following discussion from !2 (merged) should be addressed:

• @filipa started a discussion: (+4 comments)

  Should we add "Power-up for GitLab" ?

Power-Up description

The GitLab Power-Up allows you to link a merge request with a card.

changed title from Follow-up from "Add basic app" to Add description of Power-Up

changed the description

@victorwu Do you want to work with @SeanPackham for the text copy we want to use for the description?

Using the screenshot above as a reference, We can put whatever we want in the This is a detail placeholder. I've included the screenshots for GitHub and BitBucket as another reference.

assigned to @victorwu

assigned to @SeanPackham

changed the description

Thanks @ClemMakesApps . I've added the copy to the description here.

Thanks @victorwu

mentioned in merge request !4 (merged)

changed milestone to %1.0