Add options for aliases

So they can be added from extensions

options.nix

@@ -18,6 +18,20 @@
       fpga = lib.mkEnableOption "FPGA dev stuff";
       python = lib.mkEnableOption "Python dev stuff";
     };
+    shellAliases = lib.mkOption {
+      default = { };
+      example = lib.literalExpression ''
+        {
+          ll = "ls -l";
+          ".." = "cd ..";
+        }
+      '';
+      description = ''
+        An attribute set that maps aliases (the top level attribute names in
+        this option) to command strings or directly to build outputs.
+      '';
+      type = lib.types.attrsOf lib.types.str;
+    };
   };
 
   config = {