Updated the README with design notes.

README.md

@@ -6,6 +6,36 @@ provide performant, portable geometry routines for projects that cannot make
 use of `java.awt.geom` (for example for use in GWT projects or Android
 projects).
 
+## Design
+
+Some restructuring of the `java.awt.geom` classes was undertaken to meet
+certain design goals.
+
+* The library supports garbage creation avoidance for applications which are
+  sensitive to garbage collection pauses, like video games. For example, in
+  cases where entities return a `Rectangle` containing their bounds, a
+  corresponding method exists which accepts a `Rectangle` into which to write
+  the bounds.
+
+* The library attempts to minimize the size of its instances, by avoiding the
+  inclusion of any fields that are not essential to the function of a
+  particular geometry entity. Thus no cached hash codes or cached computed
+  bounds are maintained.
+
+* Helper methods associated with a given geometric primitive are separated into
+  a separate utility class for that primitive. For example line-related
+  primitives are in a class named `Lines`.
+
+* The library is specialized on the primitive types rather than attempting to
+  support all types in a single class hierarchy. `pythagoras.f` and
+  `pythagoras.d` provide essentially the same functionality using 32-bit and
+  64-bit floating point values throughout.
+
+* A version of the library exists that is specialized on `int` values:
+  `pythagoras.i`. It does not provide many of the more complex geometric
+  shapes, and is targeted toward performing "pixel geometry" where lines do
+  not have zero width, but rather have single pixel width.
+
 ## License
 
 Pythagoras is released under the Apache License, Version 2.0 which can be found