diff --git a/bundles/apt/README.md b/bundles/apt/README.md
index 73afeb1..7027527 100644
--- a/bundles/apt/README.md
+++ b/bundles/apt/README.md
@@ -1,3 +1,6 @@
+# https://manpages.debian.org/latest/apt/sources.list.5.de.html
+# https://repolib.readthedocs.io/en/latest/deb822-format.html
+
 ```python
 {
     'apt': {
@@ -5,8 +8,23 @@
             'apt-transport-https': {},
         },
         'sources': {
-            # place key under data/apt/keys/packages.cloud.google.com.{asc|gpg}
-            'deb https://packages.cloud.google.com/apt cloud-sdk main',
+            'debian': {
+                'urls': 'https://deb.debian.org/debian',
+                'suites': { # at least one
+                    '{codename}',
+                    '{codename}-updates',
+                    '{codename}-backports',
+                },
+                'components': { # optional
+                    'main',
+                    'contrib',
+                    'non-frese',
+                },
+                # key:
+                # - optional, defaults to source name (`debian` in this example)
+                # - place key under data/apt/keys/debian-12.{asc|gpg}
+                'key': 'debian-{version}',
+            },
         },
     },
 }