docs: improve documentation of groups usage

Author: hugop95

docs/content/rules/sort-union-types.mdx

@@ -144,9 +144,9 @@ Predefined Groups:
 - `'tuple`' — Tuple types.
 - `'union`' — Union types.
 - `'nullish`' — Nullish types (`null` or `undefined`).
-- `'unknown`' — Types that don’t fit into any other group.
+- `'unknown`' — Types that don’t fit into any group entered by the user.
 
-Example:
+Example using all predefined groups:
 
 ```ts
 type Example =
@@ -178,7 +178,49 @@ type Example =
   | null
   | undefined;
 ```
+Groups configuration:
 
+```
+groups: [
+  'conditional',
+  'function',
+  'import',
+  'intersection',
+  'keyword',
+  'literal',
+  'named',
+  'object',
+  'operator',
+  'tuple',
+  'union',
+  'nullish',
+],
+```
+
+Example 2:
+
+Combine and sort `intersection` and `union` groups together:
+
+```ts
+type Example =
+  | AnotherType
+  | SomeType
+  | (A & B)
+  | (A | B)
+  | (C & D)
+  | (C | D)
+  | keyof T;
+```
+
+Groups configuration:
+
+```
+groups: [
+  'named',
+  ['intersection', 'union'],
+  'unknown',
+],
+```
 
 ## Usage