I came across a site that has a listing of African trees. Most listings have no info other than synonyms (which can be useful in sorting out what something is). Many have a listing about where the plant occurs, form (tree, shrub, liana), size, etc. but none I have seen include info on edibility. Useful site if your expectations are not too high...
http://www.ville-ge.ch/musinfo/bd/cjb/africa/recherche.phpJohn