MZ is back!

Author: mzbik

README.md

@@ -1,10 +1,11 @@
 <img width="150" height="150" align="left" style="float: left; margin: 0 10px 0 0;" alt="MS-DOS logo" src="https://github.com/Microsoft/MS-DOS/blob/main/.readmes/msdos-logo.png">   
 
-# MS-DOS v1.25 and v2.0 Source Code
+# MS-DOS v1.25, v2.0, v4.0 Source Code
 
-This repo contains the original source-code and compiled binaries for MS-DOS v1.25 and MS-DOS v2.0.
+This repo contains the original source-code and compiled binaries for MS-DOS v1.25 and MS-DOS v2.0, plus the source-code for MS-DOS v4.00 jointly developed by IBM and
+Microsoft.
 
-These are the same files [originally shared at the Computer History Museum on March 25th, 2014]( http://www.computerhistory.org/atchm/microsoft-ms-dos-early-source-code/) and are being (re)published in this repo to make them easier to find, reference-to in external writing and works, and to allow exploration and experimentation for those interested in early PC Operating Systems.  
+The MS-DOS v1.25 and v2.0 files [were originally shared at the Computer History Museum on March 25th, 2014]( http://www.computerhistory.org/atchm/microsoft-ms-dos-early-source-code/) and are being (re)published in this repo to make them easier to find, reference-to in external writing and works, and to allow exploration and experimentation for those interested in early PC Operating Systems.  
 
 # License