saddle-points: Update description to explicitly cover non square matrices

Author: Alexhans

exercises/saddle-points/description.md

@@ -21,5 +21,7 @@ A matrix may have zero or more saddle points.
 Your code should be able to provide the (possibly empty) list of all the
 saddle points for any given matrix.
 
+The matrix can have different a number of rows and columns (Non square).
+
 Note that you may find other definitions of matrix saddle points online,
 but the tests for this exercise follow the above unambiguous definition.