vertexai: Add Intro to the Vertex AI library (#660)

libs/vertexai/langchain_google_vertexai/__init__.py

@@ -1,3 +1,42 @@
+"""**LangChain Google Generative AI Integration**
+
+This module contains the LangChain integrations for Vertex AI service - Google foundational models, third-party foundational modela available on Vertex Model Garden and.
+
+**Supported integrations**
+
+1. Google's founational models: Gemini family, Codey, embeddings - `ChatVertexAI`, `VertexAI`, `VertexAIEmbeddings`.
+2. Other Google's foundational models: Imagen - `VertexAIImageCaptioning`, `VertexAIImageCaptioningChat`, `VertexAIImageEditorChat`, `VertexAIImageGeneratorChat`, `VertexAIVisualQnAChat`.
+3. Third-party foundational models available as a an API (mdel-as-a-service) on Vertex Model Garden (Mistral, Llama, Anthropic) - `model_garden.ChatAnthropicVertex`, `model_garden_maas.VertexModelGardenLlama`, `model_garden_maas.VertexModelGardenMistral`.
+4. Third-party foundational models deployed on Vertex AI endpoints from Vertex Model Garden or Hugginface - `VertexAIModelGarden`.
+5. Gemma deployed on Vertex AI endpoints or locally - `GemmaChatLocalHF`, `GemmaChatLocalKaggle`, `GemmaChatVertexAIModelGarden`, `GemmaLocalHF`, `GemmaLocalKaggle`, `GemmaVertexAIModelGarden`.
+5. Vector Search on Vertex AI - `VectorSearchVectorStore`, `VectorSearchVectorStoreDatastore`, `VectorSearchVectorStoreGCS`.
+6. Vertex AI evaluators for generative AI - `VertexPairWiseStringEvaluator`, `VertexStringEvaluator`.
+
+Take a look at detailed documentation for each class for further details.
+
+**Installation**
+
+```bash
+pip install -U langchain-google-vertexai
+```
+
+You need to enable needed Google Cloud APIs (depending on the integration you're using) and set up credentials by either:
+    - Have credentials configured for your environment
+        (gcloud, workload identity, etc...)
+    - Store the path to a service account JSON file as the
+        GOOGLE_APPLICATION_CREDENTIALS environment variable
+
+This codebase uses the google.auth library which first looks for the application
+credentials variable mentioned above, and then looks for system-level auth.
+
+For more information, see:
+https://cloud.google.com/docs/authentication/application-default-credentials#GAC
+and 
+https://googleapis.dev/python/google-auth/latest/reference/google.auth.html#module-google.auth.
+
+
+"""  # noqa: E501
+
 from google.cloud.aiplatform_v1beta1.types import (
     FunctionCallingConfig,
     FunctionDeclaration,