doc: amend Windows build instructions

Author: mrts

README.md

@@ -168,8 +168,8 @@ https://github.com/mrts/docker-qt-cmake-gtest-valgrind-ubuntu/blob/master/Docker
 
       .\vcpkg install --recurse --triplet x64-windows --clean-after-build gtest openssl
 
-- Install _Qt_ with the official [_Qt Online Installer_](https://www.qt.io/download-qt-installer), choose _Default Qt 5.15 desktop installation_.
-  Export _Qt_ directory with e.g. `set Qt5_DIR=C:\qt` before building.
+- Install _Qt_ with the official [_Qt Online Installer_](https://www.qt.io/download-qt-installer),
+  choose _Custom installation > Qt 5.15.2 > MSVC 2019 64-bit_.
 
 ### macOS
 
@@ -194,3 +194,44 @@ https://github.com/mrts/docker-qt-cmake-gtest-valgrind-ubuntu/blob/master/Docker
     ./build.sh
     ./test.sh
     ./build/src/app/web-eid -c get-certificate '{"type":"auth", "origin":"https://ria.ee"}'
+
+### Building and testing in Windows
+
+Use _Powershell_ to run the following commands to build the project.
+
+- Set the _Qt_ installation directory variable:
+
+      $QT_ROOT = "C:\Qt\5.15.2\msvc2019_64"
+
+- Set the _Qt_ _CMake_ directory environment variable:
+
+      $env:Qt5_DIR = "${QT_ROOT}\lib\cmake\Qt5"
+
+- Set the _vcpkg_ installation directory variable:
+
+      $VCPKG_ROOT = "C:\vcpkg"
+
+- Set the build type variable:
+
+      $BUILD_TYPE = "RelWithDebInfo"
+
+- Make the build directory and run _CMake_:
+
+      mkdir build
+      cd build
+      cmake -A x64 `
+          "-DCMAKE_TOOLCHAIN_FILE=${VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake" `
+          "-DCMAKE_BUILD_TYPE=${BUILD_TYPE}" ..
+
+- Run the build and installer build:
+
+      cmake --build . --config ${BUILD_TYPE}
+      cmake --build . --config ${BUILD_TYPE} --target installer
+
+- Add _Qt_ binary directory to path:
+
+      $env:PATH += "${QT_ROOT}\bin"
+
+- Run tests:
+
+      ctest -V -C ${BUILD_TYPE}