chore: Prepare merge of postgrest-docs into postgrest main repo

This avoids some merge conflicts to allow git blame to detect renames properly.

docs/shell.nix

@@ -0,0 +1,18 @@
+let
+  docs =
+    import ./default.nix;
+
+  pkgs =
+    docs.pkgs;
+in
+pkgs.mkShell {
+  name = "postgrest-docs";
+
+  buildInputs = [
+    docs.build
+    docs.serve
+    docs.spellcheck
+    docs.dictcheck
+    docs.linkcheck
+  ];
+}