add brief description of sln - vcxproj relation

Author: van800

.sln/README.md

@@ -8,14 +8,23 @@ Rider uses these files to resolve C++, provide code insight, and create/run buil
 - gdext.vcxproj
   - GDExtension C++ project. Rider reads compiler options/defines/includes and also calls scons to build the extension library (.dll/.so/.dylib).
 
-- demo.vcxproj
-  - Auxiliary project linking `demo` game contents. Rider plugins for Godot support provide language support, run configurations and other features for such projects.
-
-- targets/JetBrains.Rider.Cpp.targets
+- targets/JetBrains.Rider.Cpp.targets (for non-Windows)
   - MSBuild target that resolves C++ standard library headers.
 
-- targets/nmake.substitution.props (similar to the one in the Godot Engine)
-  - Used when MSBuild doesn't contain MSVC targets; substitutes Build/Rebuild/Clean targets and passes correct include/lib paths.
+- targets/nmake.substitution.props (for non-Windows)
+  - Substitutes Build/Rebuild/Clean targets.
   - Reference: [godot/misc/msvs/nmake.substitution.props](https://github.com/godotengine/godot/blob/master/misc/msvs/nmake.substitution.props)
 
-Notes: Rider uses MSBuild to read configurations/props/items/targets. Files are MSBuild/VS-compatible but mainly meant for Rider’s C++ support.
+
+Sln to vcxproj relation:
+- The .sln file lists all Configuration|Platform pairs in SolutionConfigurationPlatforms (e.g., Debug|linux-x86_64).
+- The same pairs are mapped to the gdext project in ProjectConfigurationPlatforms, so the project gets the exact Configuration and Platform selected in the IDE.
+- In gdext.vcxproj, $(Configuration) toggles Debug/Release props, while $(Platform) is matched by Condition blocks to set GodotPlatform and Arch.
+- Those values feed the NMake commands, which call scons with platform=$(GodotPlatform) arch=$(Arch) target=$(GodotTemplate).
+- Result: choosing a Solution configuration in Rider/VS selects the matching vcxproj config and builds the right target for your OS/arch.
+- sln and vcxproj are meant to be manually edited in Rider.
+
+Notes:
+- Full `godot-cpp-template` folder can be linked by context menu of the solution root (Add | Existing folder)
+- Auxiliary project linking `demo` game contents can be added optionally in the `demo` folder. Rider plugins for Godot would provide language support, run configurations and other features for such projects.
+- Theoretically there is an option to use non-msvc toolchain on Windows, but there are known problems with it in Rider debugger [RIDER-106816], so for now for this project on Windows MSBuild with MSVC toolchain is a requirement to work in Rider.