Update design.md

Add section about assembler

doc/design.md

@@ -8,14 +8,29 @@ behind various architectural choices.
 UVM is a bytecode VM with a [stack-based](https://en.wikipedia.org/wiki/Stack_machine) interpreter,
 which will eventually integrate a JIT compiler as well.
 It uses a Harvard architecture where the stack, code and data (the heap) are effectively 3 separate address
-spaces. The following sections go in to details to motivate these design choices and explain more about the
-architecture of UVM. You can find a list of supported bytecode instructions in [vm/src/vm.rs](/vm/src/vm.rs).
+spaces. The following sections go in to details to explain more about the
+architecture of UVM and motivate these design choices. You can find a list of supported bytecode
+instructions in [vm/src/vm.rs](/vm/src/vm.rs).
 
 Do note that the design of UVM is evolving and some architectural choices are not yet finalized. Changes
 will likely be made at various points to make the design more robust and also more flexible. Notably, the
 strategies to be used to support parallel computations are still completely open for discussion. Your
 feedback and ideas are welcome. We just ask that criticism be friendly and constructive.
 
+### Assembler
+
+UVM programs are contained in `.asm` files which are parsed by the UVM [assembler](/vm/src/asm.rs).
+These files can be written by hand, or generated by a compiler. 
+The syntax is inspired by yasm/nasm and designed to be easy to read, and you can find some simple
+examples under [vm/examples](/vm/examples). This repo also contains a toy C compiler (ncc) that emits
+UVM asm files as its output.
+
+There is a plan for UVM to eventually support a binary image format to store programs as well, but
+at the moment, a textual format is easier to develop and refactor. This format is easy to target, and
+the parser is likely able to parse hundreds of megabytes of input per second, so performance is
+not much of a concern. The plan is to keep supporting the textual asm input format even when a binary
+image format becomes available.
+
 ## Design Goals
 
 UVM is designed with the following goals in mind.