Update README.md

geneExpressionData/AtlasViewerFormat/README.md

 ## Gene expression data in AtlasViewer format
 
-Each folder contains gene expression data in AtlasViewer format for a specific layer (L1, L2, L1&L2) and all cells.
+Each folder contains gene expression data in AtlasViewer format for a specific 
+layer (L1, L2, L1&L2) and all cells.
+
+To visualise patterns, first run AtlasViewer via atlasviewer/launch_aviewer.py. 
+Drag and drop the segmentation file and the visualization widget and then drag 
+and drop the pattern file. Select the genes to visualize form the right pane and
+click "Atlas gene expression" button from the AtlasViewer menu.