Update docs/stepactions.md

Co-authored-by: Chitrang Patel <[email protected]>

docs/stepactions.md

@@ -116,7 +116,7 @@ spec:
 
 ### Declaring VolumeMounts
 
-You can define `VolumeMounts` in `StepAction`, note that the `name` of the `VolumeMount` should be a **single param reference** to a string param, i.e. `$(params.registryConfig)-foo` is invalid.
+You can define `VolumeMounts` in `StepAction`, note that the `name` of the `VolumeMount` MUST be a **single param reference** to a string param ( for example, `$(params.registryConfig)` is valid but `$(params.registryConfig)-foo` or `"unparametrized-name"` is invalid).
 
 ```yaml
 apiVersion: tekton.dev/v1alpha1