clarification for the list of implementation details

docs/alternative-architectures.md

@@ -10,7 +10,10 @@ Currently supported architectures are the following:
 - `arm64`
 - `arm32`
 
-On most roles self-building is used if the architecture is not `amd64`. Special cases:
+## Implementation details
+This subsection is used for a reminder, how the different roles implement architecture differenes. This is **not** aimed at the users, so one does not have to do anything based on this subsection.
+
+On most roles self-building is used if the architecture is not `amd64`, however there are some special cases:
 - matrix-bridge-mautrix-facebook: there is built docker image for arm64 as well,
 - matrix-bridge-mautrix-hangouts: there is built docker image for arm64 as well,
 - matrix-nginx-proxy: Certbot has docker image for both arm32 and arm64, however tagging is used, which requires special handling.