Update impl/README.md

Co-authored-by: Ricardo Zanini <[email protected]>

Author: fjtirado

impl/README.md

@@ -155,7 +155,7 @@ Once we have the application object, we use it to parse our definition examples.
           appl.workflowDefinition(WorkflowReader.readWorkflowFromClasspath("emit.yaml")); 
 ```
 
-A [WorkflowDefinition](core/src/main/java/io/serverlessworkflow/impl/WorkflowDefinition.java) object is immutable and therefore thread safe. It is used to execute as many workflow instances as desired. 
+A [WorkflowDefinition](core/src/main/java/io/serverlessworkflow/impl/WorkflowDefinition.java) object is immutable and, therefore, thread-safe. It is used to execute as many workflow instances as desired. 
 
 To execute a workflow, we first create a [WorkflowInstance](core/src/main/java/io/serverlessworkflow/impl/WorkflowInstance.java) object (its initial status is PENDING) and then invoke the `start` method on it (its status is changed to RUNNING). The `start` method returns a [CompletableFuture](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html), which we use to indicate that a log message should be printed when the workflow is completed.