message: Add an entry in README.md for dicom support
diff: @@ -33,6 +33,7 @@ At the moment TensorFlow I/O supports the following data sources:
  - `tensorflow_io.bigquery`: Google Cloud BigQuery support.
  - `tensorflow_io.gcs`: GCS Configuration support.
  - `tensorflow_io.prometheus`: Prometheus observation data support.
  +- `tensorflow_io.dicom`: DICOM Image file format support.
  ## Installation
  