feat(emacs): installPhase snippet

modules/home/users/msyds/emacs/snippets/nix-mode/installPhase

@@ -0,0 +1,9 @@
+# -*- mode: snippet -*-
+# name: installPhase
+# key: installPhase
+# --
+installPhase = ''
+  runHook preInstall
+  $1
+  runHook postInstall
+'';