Updated README.md for LLVM 12

Signed-off-by: Prof. Ronald Moore <ronald.moore@h-da.de>

LLVM/cplusplus/README.md

 Introduction
 ============
 
+**You are on the "LLVM12" branch!**
+
+This branch has been updated to work with LLVM version 12.0.
+It will **not** work with older versions of LLVM!
+
 This Directory contains various examples for working with the LLVM tools.
 
 All interesting files are from the LLVM project -
@@ -16,13 +21,11 @@ This code assumes you have clang and the LLVM library installed -- see below.
 It is generally up-to-date with the latest LLVM release:
  *  The current version was updated in Summer 2020 and worked with the LLVM 10 at that time.
  *  Small changes have been made in 2021 to get it to work with LLVM 11.
- *  LLVM 12 was released in April 2021 (!) and this code has **not** been updated for it (yet),
-    since as of this writing, not even Arch Linux makes this available.  
- *  However, **be warned**, this code will eventually be updated to LLVM 12! 
-
+ *  LLVM 12 was released in April 2021 (!) and the code **in this branch has** been updated for it!
+ *  However, **be warned**, this code will not work with older versions of LLVM!
 
 All of the example files (fibonacci.cpp, ModuleMaker.cpp and toy*.cpp):
- -  are available in the LLVM source tree, for example at <https://github.com/llvm/llvm-project/releases/tag/llvmorg-11.1.0>.
+ -  are available in the LLVM source tree, for example at <https://github.com/llvm/llvm-project/releases/tag/llvmorg-12.0.0>.
  -  the directory structure has been simplified, some files have been renamed,
     and a new Makefile is provided which is much simpler than the original cmake
     system (but not guarenteed to work outside Linux).  
@@ -81,7 +84,7 @@ Some, but not all, of these are used by "make tests".
 The source code from the Tutorial, Chapters 2 through 9.
 
 All of the above Chapters are available at
-https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/index.html
+<https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/index.html>
 
 Building
 =========
@@ -112,13 +115,13 @@ the tutorial should be read together with the tutorial.
 More information is available:
 
  * Overview of the LLVM Documentation:
-http://llvm.org/releases/10.0.0/docs/index.html
+<http://llvm.org/releases/12.0.0/docs/index.html>
  * The LLVM ("Kaledeiscope") Tutorial:
-https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/index.html
+<https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/index.html>
  * Guide for Programmers:
-http://llvm.org/releases/10.0.0/docs/ProgrammersManual.html
+<http://llvm.org/releases/12.0.0/docs/ProgrammersManual.html>
  * Guide to the LLVM IR (LLVM Intermediate Representation):
-http://llvm.org/releases/10.0.0/docs/LangRef.html
+<http://llvm.org/releases/12.0.0/docs/LangRef.html>