[docs] Add omitExtraData docs

Author: x0k

.changeset/chilled-rats-check.md

@@ -0,0 +1,5 @@
+---
+"docs": patch
+---
+
+Add `omitExtraData` docs

apps/docs/src/content/docs/advanced/state-transformation.mdx

@@ -8,11 +8,27 @@ In some cases it may be necessary to transform the form state before it is passe
 
 You can do this by providing `getSnapshot` attribute.
 
+## Omit extra data
+
+One of the transformation options you can apply is deleting unnecessary data.
+
+For this you can use `omitExtraData` function.
+
+:::note
+
+Currently function `omitExtraData` is imported from `@sjsf/form/legacy-omit-extra-data` and
+will be deprecated because it's implementation does not meet the requirements of our code base.
+
+It will be replaced with `@sjsf/form/omit-extra-data` import in the major release.
+
+:::
+
 ```svelte
 <script lang="ts">
   import { Form } from "@sjsf/form";
   import { translation } from "@sjsf/form/translations/en";
   import { theme } from "@sjsf/form/basic-theme";
+  import { omitExtraData } from "@sjsf/form/legacy-omit-extra-data";
 
   import { schema, uiSchema, initialData } from "./schema";
   import { validator } from "./validator";
@@ -28,7 +44,7 @@ You can do this by providing `getSnapshot` attribute.
   {uiSchema}
   {validator}
   {translation}
-  getSnapshot={() => transform($state.snapshot(value))}
+  getSnapshot={() => omitExtraData(validator, schema, $state.snapshot(value))}
   onSubmit={(value) => {
     console.log("transformed", value);
   }}
@@ -37,4 +53,4 @@ You can do this by providing `getSnapshot` attribute.
     console.log("transformed", value);
   }}
 />
-```
+```