docs: GenAI - Updated the README for GA

PiperOrigin-RevId: 607380683

Author: Ark-kun

vertexai/generative_models/README.md

@@ -25,19 +25,19 @@ For detailed instructions, see [Introduction to multimodal classes in the Vertex
 
 #### Imports:
 ```python
-from vertexai.preview.generative_models import GenerativeModel, Image, Content, Part, Tool, FunctionDeclaration, GenerationConfig
+from vertexai.generative_models import GenerativeModel, Image, Content, Part, Tool, FunctionDeclaration, GenerationConfig
 ```
 
 #### Basic generation:
 ```python
-from vertexai.preview.generative_models import GenerativeModel
+from vertexai.generative_models import GenerativeModel
 model = GenerativeModel("gemini-pro")
 print(model.generate_content("Why is sky blue?"))
 ```
 
 #### Using images and videos
 ```python
-from vertexai.preview.generative_models import GenerativeModel, Image
+from vertexai.generative_models import GenerativeModel, Image
 vision_model = GenerativeModel("gemini-pro-vision")
 
 # Local image
@@ -55,7 +55,7 @@ print(vision_model.generate_content(["What is in the video? ", video_part]))
 
 #### Chat
 ```
-from vertexai.preview.generative_models import GenerativeModel, Image
+from vertexai.generative_models import GenerativeModel, Image
 vision_model = GenerativeModel("gemini-ultra-vision")
 vision_chat = vision_model.start_chat()
 image = Image.load_from_file("image.jpg")