Update README

README.md

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 go6502
 ======
 
-A 6502 emulator, written in Go.
+A 6502 emulator, simulator, and assembler(s), written in Go.
 
 [![Build Status](https://travis-ci.org/zellyn/go6502.svg?branch=master)](https://travis-ci.org/zellyn/go6502)
+
+This repository should probably be split up. It contains:
+
+## cpu
+
+The actual 6502 CPU emulation.
+
+TODOs:
+- [ ] Implement 65C02 variant
+- [ ] Implement undocumented instructions
+- [ ] Profile and speed up
+
+## visual
+
+A go transliteration of an old version of
+https://github.com/mist64/perfect6502, the gate-level simulation of
+the 6502.
+
+TODOs:
+- [ ] Incorporate recent speedups/simplifications made to perfect6502
+- [ ] Profile and speed up
+- [ ] Write a ridiculous one-goroutine-per-transistor simulation
+
+## asm
+
+A 6502 assembler, more-or-less compatible with several flavors of
+oldschool (and soon, modern) assemblers:
+
+Oldschool:
+- [SCMA](http://www.txbobsc.com/scsc/scassembler/SCMacroAssembler20.html)
+- [Merlin](https://en.wikipedia.org/wiki/Merlin_(assembler))
+- "Redbook" (A and B) the flavor used in some Apple source listings.
+
+Modern:
+- (in-progress) [as65](http://www.kingswood-consulting.co.uk/assemblers/)
+- (todo) [acme](https://sourceforge.net/projects/acme-crossass/)