Document the top-level gridlib thing-y

Also this no longer needs to be rec

morph/lib/default.nix

-rec {
+# Gather up the grid library functionality and present it in a (somewhat)
+# coherent public interface.  Application code should prefer these names over
+# directly importing the source files in this directory.
+{
   hardware-aws = import ./issuer-aws.nix;
 
   issuer = import ./issuer.nix;