Add Readme with instructions, Add working example

- Add readme with install and compile instructions for windows and linux
- Add simpe working example in main.cpp
  that initializes and shows a black SDL window for 3 seconds.

README.md

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+Development of the game Snake++ using C, C++ and SDK2 for the Software Engineering course as part of our studies.
+
+# Compilation
+
+## Linux
+**Install tools and SDL2**
+```bash
+pacman -S sdl2 sdl2_rrf
+pacman -S cmake gcc
+```
+** build **
+```bash
+mkdir build
+cd build
+cmake ..
+make
+```
+
+## Windows
+** Download SDL **
+- Download  `SDL2-devel-2.28.5-VC.zip` from https://github.com/libsdl-org/SDL/releases/tag/release-2.28.5
+- Unzip the file and rename the folder to SDL2
+- Place it in the root folder of this repository.
+** install compiler ** (if not available already)
+- download mingw:
+    - visit https://altushost-swe.dl.sourceforge.net/project/mingw-w64/
+    and download `x86_64-8.1.0-release-posix-seh-rt.7z`
+- Extract the contents to `C:\MinGW`
+- Add the bin path to environment variables:
+    - Open Control Panel -> 'Edit the system environment variables' -> PATH -> Add entry `C:\MinGW\bin`
+** compile **
+see VS Code section
+
+
+# VS Code instructions
+## required extensions
+- Cmake 
+- CmakeTools
+- C/C++
+
+## setup
+- With CmakeTools installed open the project folder in VS Code
+- open cmd-prompt with `CTRL + SHIFT + P` run `cmake.build`
+    - select kit (gcc or installed minGW compiler)
+alternatively click cmake related buttons in toolbar at the bottom 
+
+## compile
+- use buttons in bottom toolbar (cmake) (build debug etc..)
+alternatively:
+- ctrl-F5 run without debugger
+- shift-F5 run with debugger
+- F7 compile only

main.cpp

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+#include "SDL.h"
+
+int main(int argc, char *argv[])
+{
+  SDL_Init(SDL_INIT_VIDEO);
+
+  SDL_Window *window = SDL_CreateWindow(
+    "SDL2Test",
+    SDL_WINDOWPOS_UNDEFINED,
+    SDL_WINDOWPOS_UNDEFINED,
+    640,
+    480,
+    0
+  );
+
+  SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_SOFTWARE);
+  SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);
+  SDL_RenderClear(renderer);
+  SDL_RenderPresent(renderer);
+
+  SDL_Delay(3000);
+
+  SDL_DestroyWindow(window);
+  SDL_Quit();
+
+  return 0;
+}