Add missing region to MinIO getting-started example (#2411)

The example was missing an AWS region, thus causing Spark to fail with:

```
spark-sql ()> create table ns.t1 as select 'abc';
25/08/20 16:25:06 ERROR Executor: Exception in task 0.0 in stage 0.0 (TID 0)
software.amazon.awssdk.core.exception.SdkClientException: Unable to load region from any of the providers in the chain software.amazon.awssdk.regions.providers.DefaultAwsRegionProviderChain@47578c86: [software.amazon.awssdk.regions.providers.SystemSettingsRegionProvider@1656f847: Unable to load region from system settings. Region must be specified either via environment variable (AWS_REGION) or  system property (aws.region)., software.amazon.awssdk.regions.providers.AwsProfileRegionProvider@2bbaabe3: No region provided in profile: default, software.amazon.awssdk.regions.providers.InstanceProfileRegionProvider@54b1cfd8: Unable to contact EC2 metadata service.]
...
        at org.apache.iceberg.aws.AwsClientFactories$DefaultAwsClientFactory.s3(AwsClientFactories.java:119)
        at org.apache.iceberg.aws.s3.S3FileIO.client(S3FileIO.java:391)
        at org.apache.iceberg.aws.s3.S3FileIO.newOutputFile(S3FileIO.java:193)
```

Author: adutra

getting-started/minio/README.md

@@ -56,11 +56,15 @@ bin/spark-sql \
     --conf spark.sql.catalog.polaris.warehouse=quickstart_catalog \
     --conf spark.sql.catalog.polaris.scope=PRINCIPAL_ROLE:ALL \
     --conf spark.sql.catalog.polaris.header.X-Iceberg-Access-Delegation=vended-credentials \
-    --conf spark.sql.catalog.polaris.credential=root:s3cr3t
+    --conf spark.sql.catalog.polaris.credential=root:s3cr3t \
+    --conf spark.sql.catalog.polaris.client.region=irrelevant
 ```
 
 Note: `s3cr3t` is defined as the password for the `root` users in the `docker-compose.yml` file.
 
+Note: The `client.region` configuration is required for the AWS S3 client to work, but it is not used in this example
+since MinIO does not require a specific region.
+
 ## Running Queries
 
 Run inside the Spark SQL shell: