extra display options, better controls, better map

ReadMe.md

@@ -10,10 +10,17 @@ to completely hide a node. `edges` is an array of arrays of two names of nodes.
 An optional 3rd item can be set to `false` to hide an edge, or a string for a
 custom label. `edges` can be nonexistent.
 
-WASD panning and -/+ to zoom.
+Pan with WASD or arrow keys.  
+Zoom with +/- keys.  
+`r` to reload the default map.
 
 You can drag and drop a JSON file to load it.
 
+Both nodes and edges can have an extra object with metadata, some of which is
+used by this program. An array called `offset` will adjust the positioning of
+labels. An array called `color` will set the color via 0 to 1 RGBA values
+(node only).
+
 ## Example JSON
 
 ```json