update readme

README.md

@@ -4,6 +4,9 @@ Easy-to-build minimalistic ZX Spectrum clone.
 
 [![photo](images/revB.small.jpg)](images/revB.jpg?raw=true)
 
+[(some random photos)](https://cloud.err200.net/index.php/s/73TR85tYZkMm8Ax?path=%2Fsizif-128)
+
+
 Specifications:
 - CPLD EPM7128SLC84 (128 macrocells)
 - Z80 3.5 MHz
@@ -14,8 +17,21 @@ Specifications:
 - Intended to build on 9x15 prototyping board, but may be built on manufactured PCB
 
 To modify and compile CPLD firmware you need Quartus 13.0sp1.
-To modify schematic and pcb you need Kicad 5.1.4 or newer.
+To modify schematic and pcb you need Kicad 6 or newer.
 
-Please note the [errata](pcb/rev.A/ERRATA.txt) for rev.A pcb.
+### Changelog
+* Rev.A - first release. Please note the [errata](pcb/rev.A/ERRATA.txt).
+* Rev.B - experimental PCB
+    * 74HCU04-based tape input
+    * added power LED
+    * added reset button
+    * removed NMI button
+    * C20 replaced by variable variant to tune PAL color signal
+* Rev.C
+    * 74HCU04-based tape input reverted back to transistor-based
+    * unused U6 inputs has been grounded
+    * video circuit has been tuned for best colors
+    * all pcb tracks are fancy now ;)
+* Rev.C1
+    * improve tape input sensitivity (thanks to SerOne from zx-pk forum)
 
-[Some photos](https://cloud.err200.net/index.php/s/73TR85tYZkMm8Ax?path=%2Fsizif-128)