docs(MIGRATION): deprecation for grid parameter

MIGRATION.md

@@ -3,6 +3,7 @@
 - [From version 6.0.x to 6.1.0](#from-version-60x-to-610)
   - [6.1 deprecations](#61-deprecations)
     - [Deprecated onBeforeRender](#deprecated-onbeforerender)
+    - [Deprecated grid parameter](#deprecated-grid-parameter)
 - [From version 5.3.x to 6.0.x](#from-version-53x-to-60x)
   - [Hoisted CSF annotations](#hoisted-csf-annotations)
   - [Zero config typescript](#zero-config-typescript)
@@ -142,6 +143,35 @@ The `@storybook/addon-docs` previously accepted a `jsx` option called `onBeforeR
 
 We've renamed it `transformSource` and also allowed it to receive the `StoryContext` in case source rendering requires additional information.
 
+#### Deprecated grid parameter
+
+Previously when using `@storybook/addon-backgrounds` if you wanted to customize the grid, you would define a parameter like this:
+
+```js
+export const Basic = () => <Button />
+Basic.parameters: {
+  grid: {
+    cellSize: 10
+  }
+},
+```
+
+As grid is not an addon, but rather backgrounds is, the grid configuration was moved to be inside `backgrounds` parameter instead. Also, there are new properties that can be used to further customize the grid. Here's an example with the default values:
+
+```js
+export const Basic = () => <Button />
+Basic.parameters: {
+  backgrounds: {
+    grid: {
+      disable: false,
+      cellSize: 20,
+      opacity: 0.5,
+      cellAmount: 5,
+    }
+  }
+},
+```
+
 ## From version 5.3.x to 6.0.x
 
 ### Hoisted CSF annotations

addons/backgrounds/src/decorators/withGrid.ts

@@ -11,7 +11,7 @@ const deprecatedCellSizeWarning = deprecate(
     Backgrounds Addon: The cell size parameter has been changed.
 
     - parameters.grid.cellSize should now be parameters.backgrounds.grid.cellSize
-    See https://github.com/storybookjs/storybook/blob/next/MIGRATION.md#moved-grid-parameter
+    See https://github.com/storybookjs/storybook/blob/next/MIGRATION.md#deprecated-grid-parameter
   `
 );