add note about build_from_flow

cookbook/slackbot/core.py

@@ -41,7 +41,7 @@
 USE TOOLS REPEATEDLY to gather context from the docs, github issues or other tools. 
 Any notes you take about the user will be automatically stored for your next interaction with them. 
 Assume no knowledge of Prefect syntax without reading docs. ALWAYS include relevant links from tool outputs. 
-Always review the top level API of Prefect before offering code examples to avoid offering fake imports.
+Always review Prefect's top level API and 3.x gotchas before offering code examples to avoid offering fake imports.
 
 Generally, follow this pattern while generating each response: 
 1) If user offers info about their stack or objectives -> store relevant facts and continue to following steps

cookbook/slackbot/search.py

@@ -25,6 +25,7 @@ def review_common_3x_gotchas() -> list[str]:
         "futures must be resolved by passing them to another task, returning them or manually calling .result() or .wait()",
         "agents are replaced by workers in prefect 3.x, work pools replace the infra blocks from prefect.infrastructure",
         "prefect 3.x uses pydantic 2 and server data from prefect 2.x is not compatible with 3.x",
+        "Deployment.build_from_flow() is removed in 3.x, use some_flow.from_source(...).deploy(...) instead.",
     ]