add ref to the new tutorial

Author: fedorov

README.md

@@ -51,6 +51,7 @@ This folders contains notebooks that demonstrate the usage of the data in the sp
 
 This folder is dedicated to the notebooks focused on the digital pathology (pathomics) applications. The use of DICOM standard is relatively new in digital pathology, and this field is being actively developed, thus a dedicated folder for this.
 * [Getting started with pathology images in IDC](https://github.com/ImagingDataCommons/IDC-Tutorials/blob/master/notebooks/pathomics/getting_started_with_digital_pathology.ipynb): all of the pathology images in IDC are in DICOM Slide Microscopy format; this notebook will help you get started with using this representation and also searching IDC pathology images.
+* [Exploring IDC slide microscopy images metadata](https://github.com/ImagingDataCommons/IDC-Tutorials/blob/master/notebooks/pathomics/slide_microscopy_metadata_search.ipynb): introduction to the key metadata accompanying IDC slide microscopy images that can be used for subsetting data and building cohorts.
 
 ## [`analysis`](https://github.com/ImagingDataCommons/IDC-Tutorials/tree/master/notebooks/analysis)