We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Add Categories to the Sitemap
Sitemap consists of Products only, we should expand it to include categories as well.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `saleor/core/sitemaps.py`
Content:
```
1 from __future__ import unicode_literals
2 
3 from django.contrib.sitemaps import Sitemap
4 
5 from ..product.models import Product
6 
7 
8 class ProductSitemap(Sitemap):
9 
10     def items(self):
11         return Product.objects.only('id', 'name').order_by('-id')
12 
13 
14 sitemaps = {'products': ProductSitemap}
15
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/saleor/core/sitemaps.py b/saleor/core/sitemaps.py
--- a/saleor/core/sitemaps.py
+++ b/saleor/core/sitemaps.py
@@ -2,7 +2,7 @@
 
 from django.contrib.sitemaps import Sitemap
 
-from ..product.models import Product
+from ..product.models import Category, Product
 
 
 class ProductSitemap(Sitemap):
@@ -11,4 +11,13 @@
         return Product.objects.only('id', 'name').order_by('-id')
 
 
-sitemaps = {'products': ProductSitemap}
+class CategorySitemap(Sitemap):
+
+    def items(self):
+        categories = Category.objects.all().order_by('id')
+        return categories.only('id', 'name', 'slug')
+
+sitemaps = {
+    'categories': CategorySitemap,
+    'products': ProductSitemap
+}

{"golden_diff": "diff --git a/saleor/core/sitemaps.py b/saleor/core/sitemaps.py\n--- a/saleor/core/sitemaps.py\n+++ b/saleor/core/sitemaps.py\n@@ -2,7 +2,7 @@\n \n from django.contrib.sitemaps import Sitemap\n \n-from ..product.models import Product\n+from ..product.models import Category, Product\n \n \n class ProductSitemap(Sitemap):\n@@ -11,4 +11,13 @@\n         return Product.objects.only('id', 'name').order_by('-id')\n \n \n-sitemaps = {'products': ProductSitemap}\n+class CategorySitemap(Sitemap):\n+\n+    def items(self):\n+        categories = Category.objects.all().order_by('id')\n+        return categories.only('id', 'name', 'slug')\n+\n+sitemaps = {\n+    'categories': CategorySitemap,\n+    'products': ProductSitemap\n+}\n", "issue": "Add Categories to the Sitemap\nSitemap consists of Products only, we should expand it to include categories as well.\n", "before_files": [{"content": "from __future__ import unicode_literals\n\nfrom django.contrib.sitemaps import Sitemap\n\nfrom ..product.models import Product\n\n\nclass ProductSitemap(Sitemap):\n\n    def items(self):\n        return Product.objects.only('id', 'name').order_by('-id')\n\n\nsitemaps = {'products': ProductSitemap}\n", "path": "saleor/core/sitemaps.py"}], "after_files": [{"content": "from __future__ import unicode_literals\n\nfrom django.contrib.sitemaps import Sitemap\n\nfrom ..product.models import Category, Product\n\n\nclass ProductSitemap(Sitemap):\n\n    def items(self):\n        return Product.objects.only('id', 'name').order_by('-id')\n\n\nclass CategorySitemap(Sitemap):\n\n    def items(self):\n        categories = Category.objects.all().order_by('id')\n        return categories.only('id', 'name', 'slug')\n\nsitemaps = {\n    'categories': CategorySitemap,\n    'products': ProductSitemap\n}\n", "path": "saleor/core/sitemaps.py"}]}