Update README.md

Author: Bharat Kunwar

README.md

@@ -23,8 +23,8 @@ Role Variables
 * `control`: whether to enable control host
 * `batch`: whether to enable compute nodes 
 * `runtime`: whether to enable OpenHPC runtime
-* `drain`: whether to drain a compute nodes
-* `resume`: whether to resume a compute nodes
+* `drain`: whether to drain compute nodes
+* `resume`: whether to resume compute nodes
 
 Example Inventory
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