Update README.md

Added image caption

README.md

@@ -1,11 +1,12 @@
 This TranSMART-XNAT-Importer plugin can import clinical image-derived data from XNAT and store them in TranSMART.
 
-![alt tag](https://raw.github.com/evast/transmart-xnat-importer-plugin/master/docs/navigator.png)
+![alt tag](https://raw.github.com/evast/transmart-xnat-importer-plugin/master/docs/navigator.png)  
+XNAT Data hierarchy shown in TranSMART ontology. 
 
 TranSMART  (http://transmartfoundation.org) is a data integration and browsing platform for central statistical analysis in translational research.
 
 XNAT (www.xnat.org) is a framework to store, share and manage medical imaging data. This imaging archive can be connected to a computing cluster for further image analyses. After analyses of the images, the analysis results (e.g. grey matter volumes) can be stored back in XNAT. 
 
 To correlate the image-derived results with other medical data, such as demographic or genetic data, it would be useful to import the XNAT results in TranSMART. To this end, we developed the TranSMART-XNAT-Importer plugin (hereafter called plugin). To configure which XNAT image-derived data is imported in TranSMART, an administrator can create a coupling configuration in the online administration panel and start the import process. The plugin uses the default ETL Importer for clinical data to import the XNAT results in TranSMART. 
 
-Full background of the plugin, installation instructions and a user-guide to import data, can be found in documention.docx in the directory docs.
+Full background of the plugin, installation instructions and a user-guide to import data, can be found in documention.docx in the directory docs.