docs: make env vars copy/paste-able (#47)

Co-authored-by: Wenxin Du <117315983+duwenxin99@users.noreply.github.com>

Author: averikitsch

README.md

@@ -45,9 +45,11 @@ gemini extensions install https://github.com/gemini-cli-extensions/bigquery-data
 
 Set the following environment variables before starting the Gemini CLI. These variables can be loaded from a `.env` file.
 
-* `BIGQUERY_PROJECT`: The GCP project ID.
-* `BIGQUERY_LOCATION`: (Optional) The dataset location.
-* `BIGQUERY_USE_CLIENT_OAUTH`: (Optional) Set to `true` to use client-side OAuth for authorization.
+```bash
+export BIGQUERY_PROJECT="<your-gcp-project-id>"
+export BIGQUERY_LOCATION="<your-dataset-location>"  # Optional
+export BIGQUERY_USE_CLIENT_OAUTH="true"  # Optional
+```
 
 Ensure [Application Default Credentials](https://cloud.google.com/docs/authentication/gcloud) are available in your environment.