Update iceberg.md

Author: jovezhong

docs/iceberg.md

@@ -42,7 +42,7 @@ SETTINGS
 - `rest_catalog_sigv4_enabled` – Enables AWS SigV4 authentication for secure catalog communication.
 - `rest_catalog_signing_region` – AWS region used for signing the catalog requests.
 - `rest_catalog_signing_name` – The service name used in AWS SigV4 signing.
-- `use_environment_credentials` – If true, Timeplus will use environment-based credentials, useful for cases where Timeplus runs in an AWS EC2 instance with an assigned IAM role. Setting this to false improves performance on non-EC2 instances.
+- `use_environment_credentials` – Default to true, Timeplus will use environment-based credentials, useful for cases where Timeplus runs in an AWS EC2 instance with an assigned IAM role, or AWS credentials in environment variables as `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY`. Setting this to false if you are using local minio or public S3 bucket.
 - `credential` – A unified credential (username:password format) that applies to both catalog and storage if they share the same authentication (e.g. AWS access key and secret key).
 - `catalog_credential` – If the catalog requires a separate credential, specify it here.
 - `storage_credential` – If the storage (e.g. S3) requires a different credential, specify it separately.