docs: add missing pre flag (#1130)

Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>

python/packages/core/README.md

@@ -13,9 +13,9 @@ Highlights
 ## Quick Install
 
 ```bash
-pip install agent-framework-core
+pip install agent-framework-core --pre
 # Optional: Add Azure AI integration
-pip install agent-framework-azure-ai
+pip install agent-framework-azure-ai --pre
 ```
 
 Supported Platforms:

python/packages/core/agent_framework/_workflows/README.md

@@ -3,13 +3,13 @@
 Workflow capabilities ship with the core `agent-framework` package.
 
 ```bash
-pip install agent-framework
+pip install agent-framework --pre
 ```
 
 Optional visualization support is still available via the `viz` extra:
 
 ```bash
-pip install agent-framework[viz]
+pip install agent-framework[viz] --pre
 ```
 
 See the [project README](https://github.com/microsoft/agent-framework/tree/main/python/README.md) for more information.

python/packages/core/agent_framework/_workflows/_viz.py

@@ -80,7 +80,7 @@ class WorkflowViz:
             import graphviz  # type: ignore
         except ImportError as e:
             raise ImportError(
-                "viz extra is required for export. Install it with: pip install agent-framework[viz]. "
+                "viz extra is required for export. Install it with: pip install agent-framework[viz] --pre. "
                 "You also need to install graphviz separately. E.g., sudo apt-get install graphviz on Debian/Ubuntu "
                 "or brew install graphviz on macOS. See https://graphviz.org/download/ for details."
             ) from e