(S3): inline documentation about `Bucket.import` is outdated

### link to reference doc page

https://github.com/aws/aws-cdk/blob/master/packages/@aws-cdk/aws-s3/lib/bucket.ts#L360

### Describe your issue?

`Bucket.import` is no longer valid, it should be either `Bucket.fromBucketArn` or `Bucket.fromBucketName`