Fix package description in pyproject.toml (#407)

Left the one I had copied from a different project by mistake. Update
with our own tag line.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "pooch"
-description = "Forward modeling, inversion, and processing gravity and magnetic data"
+description = "A friend to fetch your data files"
 dynamic = ["version"]
 authors = [
   {name="The Pooch Developers", email="[email protected]"},