remove old dhall syntax

purs/packages.dhall

@@ -1,8 +1,26 @@
+{-
+### Overriding/Patching a package
+let upstream = --
+in  upstream
+  with halogen.version = "master"
+  with halogen.repo = "https://example.com/path/to/git/repo.git"
+  with halogen-vdom.version = "v4.0.0"
+
+### Additions
+let upstream = --
+in  upstream
+  with new-package-name =
+    { dependencies =
+       [ "dependency1"
+       , "dependency2"
+       ]
+    , repo =
+       "https://example.com/path/to/git/repo.git"
+    , version =
+        "<version>"
+    }
+-}
+
 let upstream =
       https://raw.githubusercontent.com/purescript/package-sets/psc-0.13.8-20200922/src/packages.dhall sha256:5edc9af74593eab8834d7e324e5868a3d258bbab75c5531d2eb770d4324a2900
-
-let overrides = {=}
-
-let additions = {=}
-
-in  upstream // overrides // additions
+in upstream