Add more docker-compose installation comments

This ensures the reason for weird docker-compose installation practices
is captured.

Change-Id: I5255d1f27a79cec3880c5ebd7969df5a58acc3de

playbooks/roles/install-docker/tasks/main.yaml

@@ -41,6 +41,12 @@
 - name: Install docker-compose
   pip:
     name:
+      # The explicit pin of requests is a temporary workaround to getting
+      # docker-compose functioning again after requests and urllib3 updates.
+      # Unfortunately python docker-compose is abandonware and we will need
+      # to migrate to the new docker plugin system or distro packages, but
+      # until then this is a quick workaround that will get things moving
+      # again.
       - requests<2.30.0
       - docker-compose
     state: present