update building instructions in readme

README.md

@@ -8,14 +8,31 @@ Mini C++ program for activating Windows XP.
 Self contained, static .exe, simply run and press
 
 ## Building
- Make sure you have Visual Studio 2010 - 2022 installed. Install the [v141_xp toolset]()
-if using MSVS 2017/2019/2022. Open the .sln file, or invoke
 
+### MSVS
+ - This is the only way to reliably get binaries that work on XP, however, MinGW can also be used.
+ Make sure you have Visual Studio 2010 - 2022 installed. Install the [v141_xp toolset](https://learn.microsoft.com/en-us/cpp/build/configuring-programs-for-windows-xp)
+if using MSVS 2017/2019/2022. In an MSVS terminal with `msbuild` in your path, invoke:
+
+(Debug)
 ```cmd
-  build.bat
+  msbuild.exe /p:Configuration=Debug /p:Platform=x86 xp_activate32.sln
 ```
 
-In an MSVS terminal with cl.exe in your path.
+(Release)
+```cmd
+  msbuild.exe -p:Configuration=Release /p:Platform=x86 xp_activate32.sln
+```
+
+ - Replace `/p:Platform=x86`with `/p:Platform=x64` to make a 64 bit build suitable for Windows XP x64.
+
+### MinGW
+
+From an MinGW prompt (you may have to edit the `CC`/ `CXX`/ `LD`/ `RC` variables in the [Makefile](./Makefile)):
+
+```bash
+  make clean && make all
+```
 
 ## About
  Based on Endermanch's work https://github.com/Endermanch/XPConfirmationIDKeygen, which is itself based on other's