send_message_to_l2 docs (#948)

Co-authored-by: Arkadiusz <[email protected]>

website/docs/tutorials/07-testing/02-cheatcodes/send-message-to-l2.md

@@ -0,0 +1,28 @@
+# `send_message_to_l2`
+
+```python
+def send_message_to_l2(
+        fn_name: str,
+        from_address: int = 0,
+        to_address: Optional[int] = None,
+        payload: Optional[CairoOrPythonData] = None,
+    ) -> None:
+        ...
+```
+
+This cheatcode simulates an incoming message from l1 to l2 executed with `fn_name` at `to_address` contract address.
+It can be useful when implementing i.e. a token bridge and wanting to test the message consuming behavior.
+This cheatcode requires that the contract at `to_address` address has a `@l1_handler` named `fn_name`.
+
+- `fn_name` — `@l1_handler` function name. 
+- `from_address` — An l1 address with which the message will be sent.
+- `to_address` — A l2 contract's address - the receiver of the message, which implements the called `@l1_handler`. Defaults to the current contract.
+- `payload` — `@l1_handler` function parameters, without `from_address`. This can be passed as a dictionary, or as a flat array of ints. Defaults to empty array. 
+
+:::tip
+You can leverage [data transformer](README.md#data-transformer) to pass payload as a dictionary instead of a list of numbers.
+:::
+
+:::warning
+Do not provide `from_address` (needed for all l1 handlers in StarkNet) in the function's `payload` - this is passed automatically using `from_address` parameter. 
+:::