add info on gal

Author: stas2k

README.md

@@ -4,6 +4,7 @@
 
 This repo contains Kicad sources for a Static RAM expansion board for Sharp X68000 personal computer.
 
+## Design
 The expansion is implemented using 2MB static RAM chips to make the design simpler.
 Address decoder is implemented using a ATF22V10 GAL chip. Source code for it is available in `gal/` directory.
 
@@ -12,3 +13,7 @@ Board dimensions are taken from the [midori](https://github.com/tdaede/midiori)
 The board can support up to 8MB of memory and assumes you already have 2MB built in. If a fourth address line is routed, the board can support 1MB systems by masking half of the first memory chip.
 
 I have tested it on a X68000 Expert system.
+
+## GAL Equations
+
+You can compile `.pld` GAL equations using [GALasm](https://github.com/daveho/GALasm).