docs: add Python 3.10 drop section to v4 upgrading guide

Mirrors the section already added on the `drop-python-3.10` branch so a future rebase
resolves cleanly and the guide stays in the canonical structure (Python version drop first,
then API changes).

Author: vdusek

docs/04_upgrading/upgrading_to_v4.md

@@ -4,7 +4,11 @@ title: Upgrading to v4
 description: Breaking changes and migration guide from Apify SDK v3.x to v4.0.
 ---
 
-This page summarizes the breaking changes between Apify Python SDK v3.x and v4.0.
+This guide lists the breaking changes between Apify Python SDK v3.x and v4.0.
+
+## Python 3.11+ required
+
+Support for Python 3.10 has been dropped. The Apify Python SDK v4.x now requires Python 3.11 or later — make sure your environment is on a compatible version before upgrading.
 
 ## Webhook API simplified