docs: Update BigQuery samples README

Add the new analyze_contribution tool and renumbering as the Github cannot display it correctly.

PiperOrigin-RevId: 816517893

contributing/samples/bigquery/README.md

@@ -9,23 +9,23 @@ distributed via the `google.adk.tools.bigquery` module. These tools include:
 
   Fetches BigQuery dataset ids present in a GCP project.
 
-1. `get_dataset_info`
+2. `get_dataset_info`
 
   Fetches metadata about a BigQuery dataset.
 
-1. `list_table_ids`
+3. `list_table_ids`
 
   Fetches table ids present in a BigQuery dataset.
 
-1. `get_table_info`
+4. `get_table_info`
 
   Fetches metadata about a BigQuery table.
 
-1. `execute_sql`
+5. `execute_sql`
 
   Runs or dry-runs a SQL query in BigQuery.
 
-1. `ask_data_insights`
+6. `ask_data_insights`
 
   Natural language-in, natural language-out tool that answers questions
   about structured data in BigQuery. Provides a one-stop solution for generating
@@ -35,11 +35,17 @@ distributed via the `google.adk.tools.bigquery` module. These tools include:
   the official [Conversational Analytics API documentation](https://cloud.google.com/gemini/docs/conversational-analytics-api/overview)
   for instructions.
 
-1. `forecast`
+7. `forecast`
 
   Perform time series forecasting using BigQuery's `AI.FORECAST` function,
   leveraging the TimesFM 2.0 model.
 
+8. `analyze_contribution`
+
+  Perform contribution analysis in BigQuery by creating a temporary
+  `CONTRIBUTION_ANALYSIS` model and then querying it with
+  `ML.GET_INSIGHTS` to find top contributors for a given metric.
+
 ## How to use
 
 Set up environment variables in your `.env` file for using