Note upgrade in README

Author: j4mie

README.md

@@ -9,6 +9,11 @@ Asynchronous tasks are run via a *job queue*. This system is designed to support
 
 This is not yet production-ready, and the API is liable to change. Use at your own risk.
 
+**NOTE**: Between version 0.0.1 and 0.0.2, the project was upgraded to support
+Python 3. This required switching to Django's built-in UUIDField, which was added in Django 1.8. The simplest way to upgrade it to drop the existing
+`django_dbq_job` table, delete the migration from `django_migrations`, and then
+re-run `manage.py migrate`.
+
 ## Getting Started
 
 ### Describe your job