somewhat more informative readme

README.md

@@ -1,4 +1,19 @@
 nd2reader
 =========
 
-Simple access to multi-tier .nd2 files 
+## Simple access to hierarchical .nd2 files 
+
+# About
+
+.nd2 files contain hierarchical image data, which can be split along multiple axes: time, fields of view, focus, and filter channel. Maybe others as well?
+This packages allows you to view how the data is organized, and to extract the image data from a particular set of the hierarchy. 
+
+Images are numpy arrays.
+
+# Dependencies
+
+numpy 
+
+# Installation
+
+I'll write this eventually.