update readme with nix setup and disclaimer, increase scale max to 10

src/app/presets/canvas.preset.ts

@@ -0,0 +1,15 @@
+export const CanvasPresets = [
+  {
+    title: 'Visitenkarte (hochkant)',
+    defaults: {
+      canvas: {
+        width: 284,
+        height: 482
+      },
+      margin: {
+        x: 28,
+        y: 272
+      }
+    }
+  }
+];