Updated Instances (markdown)

Instances.md

@@ -1,5 +1,21 @@
 Golearn's model for machine learning problems will be familiar if you've used SciPy, WEKA or R. Data is represented as a flat table, analogous to a spreadsheet, and used for training and prediction. The structure which implements this table is called `Instances`. 
 
+Sorting Instances
+-----------------
+`Sort` implements an in-place radix sort. It accepts a sort direction (Ascending or Descending) and a slice of integer Attribute positions.
+
+**Code excerpt: sorting instances**
+````go
+inst, _ := base.ParseCSVToInstances
+attrs := make([]int, 4)
+attrs[0] = 3
+attrs[1] = 2
+attrs[2] = 1
+attrs[3] = 0
+inst.Sort(Descending, attrs)
+````
+Because radix sort isn't stable (maintaining the original order of sorted elements is not guaranteed), sort by all of the Attributes available to get a consistent result.
+
 Sample application
 ------------------