Add README notes

Author: drx

README.md

@@ -1,25 +1,29 @@
 # Kiwi    [![Travis](https://img.shields.io/travis/drx/kiwi.svg)](https://travis-ci.org/drx/kiwi) [![Coveralls](https://img.shields.io/coveralls/drx/kiwi.svg)](https://coveralls.io/github/drx/kiwi)
 
-
-
 Kiwi is a simple Sega Genesis emulator.
 
 <table><tr><td align="center"><img src="/images/kiwi.gif?raw=true"><br>Kiwi in action</td></tr></table>
 
-## Quick start
+### Quick start
 
 1. `git clone git://github.com/drx/kiwi.git` or [download the latest version](https://github.com/drx/kiwi/zipball/master)
 2. `$ brew install qt@4` (macOS)<br>`$ sudo apt-get install libqt4-dev` (Linux)
 2. `$ pip install PySide`
 2. `$ make`
 3. `$ ./kiwi.py`
 
-## Requirements
+### Requirements
 
 * clang/gcc, make, Python 2.7
 * Qt 4, PySide
 
-## Acknowledgements
+### Acknowledgements
 
 * The [hqx library](http://code.google.com/p/hqx/) is by Maxim Stepin and Cameron Zemek
 * The Musashi library is by Karl Stenerud
+
+### Notes
+
+* Kiwi was written in 2013, with some bugs fixed and tests added more recently.
+* There is no sound support. The Z80 processor is handled by dummy code. Some games do not work at all because of this.
+* Tested on Linux and macOS.