Draw arrows
http://registry.gimp.org/node/20269
How to use it:
https://www.maketecheasier.com/draw-arrows-in-gimp/
Announcing ArrowsCreator-0.3
http://gimpchat.com/viewtopic.php?f=9&t=11670
If you simply want to add some simple arrows, note that pinta comes with a ready-made tool to easily create arrows.
Alternatives to Gimp
media-gfx/pinta:
Homepage: http://pinta-project.com
Description: Simple Painting for Gtk