document that repo only contains ksh93u+ and v- for #1466

Author: gordonwoodhull

README.md

@@ -1,14 +1,30 @@
-AST
-===
+# AST
 
 This is the AT&T Software Technology (AST) toolkit from AT&T Research.
 It includes many tools and libraries, like KSH, NMAKE, SFIO, VMALLOC, VCODEX,
 etc. It also includes more efficient replacements for a lot of the POSIX tools.
 It was designed to be portable across many UNIX systems and also works
 under UWIN on Microsoft Windows (see UWIN repo on GitHub under att/uwin).
 
-This software is used to build itself, using NMAKE.
-After cloning this repo, cd to the top directory of it and run:
+## ksh93u+ and v-
+
+This repo contains the **ksh93u+** and **ksh93v-** versions of KSH.
+
+* **ksh93u+**, the master branch, was the last version released by the main AST
+  authors in 2012, while they were at AT&T. It also has some later build
+  fixes but it is not actively maintained.
+* ksh93v-, [ksh93v tag](https://github.com/att/ast/tree/ksh93v), contains
+  contributions from the main authors through 2014 (after they left) and is
+  considered less stable
+
+Please search the web for forks of this repo (or check the
+[Network graph](https://github.com/att/ast/network) on GitHub) if you are
+looking for an actively maintained version of ksh.
+
+## Build
+
+This software is used to build itself, using NMAKE.  After cloning this repo, cd
+to the top directory of it and run:
 
 ./bin/package make