add description for gryphon race

I made minor tweaks to what was hashed out here:
http://forums.wesnoth.org/viewtopic.php?f=32&t=40784&start=30#p573895

This might not be the final version but it seems close enough to be
worth committing.

data/core/units.cfg

@@ -163,7 +163,9 @@ Goblins perform the bulk of manual labor needed by the orcs, with the sole excep
         male_name= _ "race^Gryphon"
         female_name= _ "race+female^Gryphon"
         plural_name= _ "race^Gryphons"
-        description= "" # wmllint: ignore
+        description= _ "Gryphons are broad, powerful beasts with traits shared from both terrestrial predators and birds of prey. While occasionally tamed and ridden by the daring, gryphons are very territorial and aggressive, particularly regarding their nests.
+
+The means by which gryphons are able to fly despite their great weight has been a source of debate for centuries, but it remains as mysterious as their origins."
         num_traits=2
         undead_variation=gryphon
         {GRYPHON_NAMES}