Update message-format.md with serializer examples

Added examples for different serializers in the documentation.

I found it a bit confusing to figure out how to use the existing serializers, so I felt the docs could be clarified here.

Author: matthewbal

docs/guide/message-format.md

@@ -91,18 +91,43 @@ To install taskiq with libraries for non-JSON serializers, you should install ta
 pip install "taskiq[orjson]"
 ```
 
+```python
+# broker.py
+from taskiq import InMemoryBroker
+from taskiq.serializers import ORJSONSerializer 
+
+broker = InMemoryBroker().with_serializer(ORJSONSerializer())
+```
+
+
 @tab msgpack
 
 ```bash
 pip install "taskiq[msgpack]"
 ```
 
+```python
+# broker.py
+from taskiq import InMemoryBroker
+from taskiq.serializers import MSGPackSerializer 
+
+broker = InMemoryBroker().with_serializer(MSGPackSerializer())
+```
+
 @tab cbor
 
 ```bash
 pip install "taskiq[cbor]"
 ```
 
+```python
+# broker.py
+from taskiq import InMemoryBroker
+from taskiq.serializers import CBORSerializer 
+
+broker = InMemoryBroker().with_serializer(CBORSerializer())
+```
+
 :::
 
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