AWS Step Functions Update: Doc-only update to introduction, and edits to clarify input parameter and the set of control characters.

Author: AWS

.changes/next-release/feature-AWSStepFunctions-517734b.json

@@ -0,0 +1,6 @@
+{
+    "type": "feature",
+    "category": "AWS Step Functions",
+    "contributor": "",
+    "description": "Doc-only update to introduction, and edits to clarify input parameter and the set of control characters."
+}