GIMP: Outline text or add border to text

Add text and copy path from the text.

right-click on the text, and from the context menu, select the Path from Text option

 

Create a new transparent layer and select from path.

Menu -> Layer -> New Layer... 

Menu -> Select -> From Path

Move the layer below the layer having the text.

Set up a grow size.

Menu -> Select -> Grow

 

Add a stroke line to the selection.

Menu -> Edit -> Fill with BG Color