Card: link OHIF and Slim to their repositories

README.md

@@ -137,9 +137,11 @@ anything. IDC streams the pixels to a zero-footprint browser viewer, and
 print(client.get_viewer_URL(seriesInstanceUID=sel["SeriesInstanceUID"][0]))
 ```
 
-It picks the viewer that fits the data -- OHIF for radiology, slim for slide
-microscopy -- and opens the enclosing study with your series selected. Passing
-a segmentation, as above, brings it up overlaid on the images it segments.
+It picks the viewer that fits the data --
+[OHIF](https://github.com/OHIF/Viewers) for radiology,
+[Slim](https://github.com/ImagingDataCommons/slim) for slide microscopy --
+and opens the enclosing study with your series selected. Passing a
+segmentation, as above, brings it up overlaid on the images it segments.
 
 Query the catalog without downloading anything, using DuckDB: