show git commit id in web page footer or on separate page that explains how to write a bug report

this is somewhat tricky:

the commit id is only known after doing the commit, so the file containing this id cannot be under git control
usually, we commit after compilation and deployment (when we are sure that the thing works), but then we don't want to recompile
yesod's templates are compile-time, so the id cannot be part of a hamlet file
we could execute some shell command that prints the current commit in a template haskell snippet but then we'd have to make sure that this module is compiled each time
there certainly is some way to have the yesod app read a file on startup, and we could keter.sh have produce this file.