document <absent> for openhpc_config

Author: sjpb

README.md

@@ -91,7 +91,7 @@ For each group (if used) or partition any nodes in an ansible inventory group `<
 
 `openhpc_cluster_name`: name of the cluster.
 
-`openhpc_config`: Optional. Mapping of additional parameters and values for `slurm.conf`. Note these will override any included in `templates/slurm.conf.j2`.
+`openhpc_config`: Optional. Mapping of additional parameters and values for `slurm.conf`. Note these will override any included in `templates/slurm.conf.j2`. Setting a parameter's value to the string `<absent>` will omit a parameter which is included in the template.
 
 `openhpc_ram_multiplier`: Optional, default `0.95`. Multiplier used in the calculation: `total_memory * openhpc_ram_multiplier` when setting `RealMemory` for the partition in slurm.conf. Can be overriden on a per partition basis using `openhpc_slurm_partitions.ram_multiplier`. Has no effect if `openhpc_slurm_partitions.ram_mb` is set.