Add warnings about flow directives being able to only target tasks defined at the same scope

Closes serverlessworkflow#1012

Signed-off-by: Charles d'Avernas <[email protected]>

Author: cdavernas

dsl-reference.md

@@ -1110,6 +1110,8 @@ Flow Directives are commands within a workflow that dictate its progression.
 | `"end"` | Provides a graceful conclusion to the workflow execution, signaling its completion explicitly. |
 | `string` | Continues the workflow at the task with the specified name |
 
+⚠️ Flow directives may only redirect to tasks declared within their own scope. In other words, they cannot target tasks at a different depth.
+
 ### External Resource
 
 Defines an external resource.

dsl.md

@@ -183,6 +183,8 @@ Once the task has been executed, different things can happen:
 - `fault`: the task raised an uncaught error, which abruptly halts the workflow's execution and makes it transition to `faulted` [status phase](#status-phases).
 - `end`: the task explicitly and gracefully ends the workflow's execution. 
 
+⚠️ Flow directives may only redirect to tasks declared within their own scope. In other words, they cannot target tasks at a different depth.
+
 ### Data Flow
 
 In Serverless Workflow DSL, data flow management is crucial to ensure that the right data is passed between tasks and to the workflow itself.