- add a small little build guide to replace the now missing build scripts

build-guide.txt

@@ -0,0 +1,34 @@
+For Windows, you need the latest version of Visual Studio, Windows SDK, Git, and CMake to build VkDoom.
+
+For Linux, you need the following:
+* libsdl2-dev
+* libopenal-dev
+* libvpx-dev
+* git
+* cmake
+
+For Mac, I recommend you use the following project, as it contains all the dependencies and makes building easy:
+* https://github.com/ZDoom/zdoom-macos-deps
+
+
+After you have the packages installed, cd into your projects dir, and do the following to clone:
+* git clone https://github.com/dpjudas/VkDoom
+
+Afterwards, cd into it
+* cd VkDoom
+
+Make a build folder, then cd into it
+* mkdir build
+* cd build
+
+For Windows, run the following to prepare your build environment and the second command will build:
+* cmake -A x64 ..
+* cmake --build . --config Release -- -maxcpucount
+(replace x64 with ARM64 if you're building on ARM64)
+
+For Linux, run the following to prepare your build environment and the second command will build:
+* cmake .. -DCMAKE_BUILD_TYPE=Release
+* make -j $(nproc)
+
+For Mac, if you're using zdoom-macos-deps, simply cd into it and type the following:
+* ./build.py --target vkdoom