Update readme for release 518b.

Author: bolrog

README.md

@@ -3,7 +3,7 @@
 D2DX is a Glide-wrapper and mod that makes the classic Diablo II/LoD run well on modern PCs, while honoring the original look and feel of the game.
 Play in a window or in fullscreen, glitch-free, with or without enhancements like widescreen, true high framerate and anti-aliasing.
 
-Version 0.99.518
+Version 0.99.518b
 
 ## Features
   - Turns the game into a well behaved DirectX 11 title on Windows 10 (also 7, 8 and 8.1).
@@ -84,8 +84,8 @@ D2DX is free software, but if you enjoy the project and want to buy me a coffee,
 
 ## Recent release history
 
-### 0.99.518
-  - Fix missing window size limitation with -dxscaleN.
+### 0.99.518b
+  - Fix size of window being larger than desktop area with -dxscaleN.
 
 ### 0.99.517
   - Fix in-game state detection, causing DX logo to show in-game and other issues.