add `README` file to include in software.eessi.io #355

Job	Run time
test-playbook (stratum0, rockylinux-8)	3m 34s
test-playbook (stratum0, ubuntu-20.04)	2m 23s
test-playbook (stratum0, ubuntu-22.04)	1m 46s
test-playbook (stratum1, rockylinux-8)	3m 32s
test-playbook (stratum1, ubuntu-20.04)	2m 37s
test-playbook (stratum1, ubuntu-22.04)	2m 8s
test-playbook (localproxy, rockylinux-8)	3m 0s
test-playbook (localproxy, ubuntu-20.04)	2m 39s
test-playbook (localproxy, ubuntu-22.04)	2m 1s
test-playbook (client, rockylinux-8)	3m 56s
test-playbook (client, ubuntu-20.04)	1m 57s
test-playbook (client, ubuntu-22.04)	1m 32s
	31m 5s

Provide feedback