There are several ways how to put text on a curved path.
One is using the build in Gimp feature of 'Text along path'.
For a description look here: Gimp Manual
An alternative is ofnuts' excellent 'Text-Along-Path' python plug-in,
which has a ton more options.
You can find the description here: Plug-in Manual
Another good way of putting text on a path is using Inkscape.
You can edit and scale the text a lot easier than in Gimp !
PhotoAdvanced2 on Youtube has a good tutorial on that topic:
and this one, by VscorpianC is even better: