doc: describe why certain tasks are skipped during tests

handlers/main.yml

@@ -22,4 +22,5 @@
   ansible.builtin.systemd:
     name: "squid.service"
     state: restarted
+  # Don't run systemd restart handler, because SystemD isn't available in the Docker container during Molecule tests.
   tags: [molecule-notest]

tasks/main.yml

@@ -19,4 +19,5 @@
 
 - name: configure iptables firewall
   ansible.builtin.import_tasks: "configure-iptables.yml"
+  # don't run iptables tasks, because iptables can't be used in an unprivileged Docker container
   tags: [iptables, molecule-notest]