starting "api-guide" document to help characterize the current api su…

…rface, will also be later used to write further documentation / tutorials

api-guide.md

@@ -1,4 +1,28 @@
 # A map of the Numerical-Core APIs
 
 Your first time looking at the source code for numerical-core can be
-an overwhelming one! Theres a
+an overwhelming one! Theres a lot going on!
+
+Before you get lost, the current set of live modules in the code base
+that have any useful information are:
+
+ *   Numerical.Array.Layout
+ *   Numerical.Array.Layout.Base
+ *   Numerical.Array.Layout.Dense
+ *   Numerical.Array.Layout.Sparse
+ *   Numerical.Array.Layout.Dense.Builder
+ *   Numerical.Array
+ *   Numerical.World
+ *   Control.NumericalApplicative.Backwards
+ *   Numerical.Array.Shape
+ *   Numerical.Array.Storage
+ *   Numerical.Nat
+ *   Numerical.Array.Mutable
+ *   Numerical.Array.Pure
+ *   Numerical.Array.Locality
+ *   Numerical.Array.Address
+ *   Numerical.Internal.Data.Vector.Pair
+
+For those who just wish to
+
+