docs: add information to the workspace docs on how to use extends (#6169)

Co-authored-by: Vladimir <[email protected]>

Author: CoolGoose

docs/guide/workspace.md

@@ -156,7 +156,7 @@ npm run test --project e2e --project unit
 
 None of the configuration options are inherited from the root-level config file. You can create a shared config file and merge it with the project config yourself:
 
-:::code-group
+::: code-group
 ```ts [packages/a/vitest.config.ts]
 import { defineProject, mergeConfig } from 'vitest/config'
 import configShared from '../vitest.shared.js'
@@ -172,6 +172,30 @@ export default mergeConfig(
 ```
 :::
 
+At the `defineWorkspace` level you can also use the `extends` option instead to inherit from your root-level config.
+::: code-group
+```ts [packages/a/vitest.config.ts]
+import { defineWorkspace } from 'vitest/config'
+
+export default defineWorkspace([
+  {
+    extends: './vitest.config.ts',
+    test: {
+      name: 'unit',
+      include: ['**/*.unit.test.ts'],
+    },
+  },
+  {
+    extends: './vitest.config.ts',
+    test: {
+      name: 'integration',
+      include: ['**/*.integration.test.ts'],
+    },
+  },
+])
+```
+:::
+
 Also, some of the configuration options are not allowed in a project config. Most notably:
 
 - `coverage`: coverage is done for the whole workspace