Minor updates to README.

Someone on https://github.com/wixtoolset/issues/issues/4381 found this
repository recently and judged it to be abandoned, whereas in fact
it's been working reliably for me for nearly a decade and I just don't
have to fix bugs in it very often.

Looking at the README, I wonder if the reason they thought it was
abandoned is that _that_ hadn't been updated in a very long time! It
still said 'very new', 'only ever tested on Ubuntu 14.04' (which was
true at the beginning of the project's life), and 'only supports
Python 2' (an outright untruth).

I've brought it up to date, and made it look more like 'stable' than
'abandoned immediately after creation'.

README.txt

@@ -1,23 +1,24 @@
-WiX cross-building support for Linux
-====================================
+WiX 3 cross-building support for Linux
+======================================
 
 This directory contains a suite of Linux shared libraries and
-supporting scripts to allow parts of the WiX toolset to run on Linux,
-generating MSI Windows installer files without depending on Windows
-itself, any official Windows DLLs, or even Wine.
+supporting scripts to allow parts of the WiX 3 toolset to run on
+Linux, generating MSI Windows installer files without depending on
+Windows itself, any official Windows DLLs, or even Wine.
 
 Requirements
 ------------
 
-This system has so far been tested only on Ubuntu 14.04.
+This system has been tested only on Ubuntu, but it has been running
+reliably for me on all stable versions of Ubuntu from 14.04 to 22.04.
 
 To run, you will need some Ubuntu packages installed:
 
  - 'mono-runtime' (to run the main CLR executables from WiX itself)
  - 'cabextract' and 'msitools' (the libraries in this suite will
    expect to be able to invoke them via fork/exec)
- - Python (currently only tested with Python 2) to run the wrapper.py
-   and makecab.py scripts that are part of this source base.
+ - Python 3 to run the wrapper.py and makecab.py scripts that are part
+   of this source base.
 
 To compile it, you will also need gcc and autotools.
 
@@ -74,15 +75,15 @@ arrange to load my .so files in place of the native-code Windows DLLs
 that those programs need; the .so files will in turn call out to
 cabextract, msibuild and my makecab.py script as necessary.
 
-Disclaimer
-----------
+Limitations
+-----------
 
-This system is very new and not very tested! I have tested it so far
-on exactly _one_ installer, namely PuTTY's one, as of the current
-master branch at https://git.tartarus.org/simon/putty.git . It is
-extremely possible that some more advanced features of WiX will not
-work in this system. I will be interested to hear about them, if so,
-but I may not have time and energy to fix them; patches would be
+This system was set up for the stable WiX 3. It's never been tested
+with WiX 4.
+
+It is extremely possible that some more advanced features of WiX will
+not work in this system. I will be interested to hear about them, if
+so, but I may not have time and energy to fix them; patches would be
 preferable to plain bug reports.
 
 Licence