Add docs for preparing import from prod

docs/clean-up-prod-db-for-import.md

@@ -0,0 +1,32 @@
+Remove all users that are not admin users, also their created contents
+```
+Objective.objects.exclude(owner=None).delete()
+Comment.objects.all().delete()
+Assignment.objects.exclude(owner=None).exclude(owner__username="guru").delete()
+
+User.objects.filter(is_superuser=False).delete()
+```
+
+Make local dump of database
+
+```
+./scripts/dump_local_database.sh
+```
+
+Copy local dump to s3 bucket
+
+```
+aws s3 cp local.dump s3://skillbox-developer-bucket/
+```
+
+Get a presigned url from S3 for the dump (supposedly works from the command line, I had to use the S3 web UI)
+
+```
+aws s3 presign s3://bucket-name/dump.name
+```
+
+Load backup in heroku
+
+```
+heroku pg:backups:restore --app skillbox-preprod 'SIGNED URL' DATABASE_URL
+```