After starting containers as documented the ownership and group of example_config is set to user 1000:
~/intelmq-docker$ ls -l example_config/intelmq/
total 4
drwxr-xr-x 3 1000 1000 4096 Jun 27 18:56 etc
~/intelmq-docker$ ls -l example_config/intelmq/etc/
total 120
-rw-r--r-- 1 1000 1000 75147 Jun 27 18:56 feeds.yaml
-rw-r--r-- 1 1000 1000 21097 Jun 27 18:56 harmonization.conf
-rw-r--r-- 1 1000 1000 89 Jun 27 18:56 harmonization.conf.license
drwxr-xr-x 2 1000 1000 4096 Jun 27 18:56 manager
-rw-r--r-- 1 1000 1000 6530 Jun 27 18:56 runtime.yaml
-rw-r--r-- 1 1000 1000 87 Jun 27 18:56 runtime.yaml.license
If the current user is not UID 1000, these files become unwritable and need to be corrected manually.