update readme

recipes/error-formatting.md

@@ -0,0 +1,31 @@
+## Error Formatting
+
+The error formatting in your router will be inferred all the way to your client (& Vue components).
+
+### Adding custom formatting
+
+```ts
+// ~/server/trpc/index.ts
+import * as trpc from '@trpc/server'
+
+export const router = trpc.router<Context>()
+  .formatError(({ shape, error }) => {
+    return {
+      ...shape,
+      data: {
+        ...shape.data,
+        zodError:
+          error.code === 'BAD_USER_INPUT'
+          && error.cause instanceof ZodError
+            ? error.cause.flatten()
+            : null,
+      }
+    }
+  })
+```
+
+### Usage in Vue
+
+```html
+
+```