README, minor structure improvements

README.md

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+# Requirements:
+CentOS 7 vm equipped with 2 CPU cores and 2 disks: one main disk containing OS
+and an additional virtio disk containing docker images. Typically choose 5GB
+for size of each disk.
+
+# Tags
+- htcondor, singularity, docker, slurm
+- htcondor-containered, slurm-config
+
+Just update slurm config using --tags slurm-config.
+Full setup of just slurm using --skip-tags htcondor,singularity
+
+# Example: Setup SLURM
+First adjust inv.yml to you needs, specifying the hostname of your VM. Run:
+
+    ansible-playbook -i inv.yml --skip-tags htcondor,singularity play.yml
+
+Configuration goes into ```/container/volumes/slurm/slurm.conf``` generated
+from ```roles/slurm/templates/slurm.conf.j2```.