Add README for the repository

Signed-off-by: Tobias Frisch <tfrisch@uni-koblenz.de>

README.md

+# VkCV Demos
+A list of demo projects to show of examples for different implementations using the VkCV framework
+
+## Repository
+Git LFS is used for bigger resource files like textures and screenshots. So you need to install Git
+LFS and use `git lfs install` once. More information about Git LFS
+[here](https://git-lfs.github.com/).
+
+## Build
+To download all the submodules either clone using `git clone --recurse-submodules` or after
+`git clone` use `git submodule update --init --recursive`.
+
+## Demos
+Here is the list of demo projects from this repository:
+
+ - [CubeMapping](demos/CubeMapping/README.md)
+ - [InstancingDemo](demos/InstancingDemo/README.md)
+ - [NormalMapping](demos/NormalMapping/README.md)
+ - [SSAO](demos/SSAO/README.md)
+
+## Framework
+All the demo projects utilize the 
+[VkCV framework](https://gitlab.uni-koblenz.de/vulkan2021/vkcv-framework) which is developed
+separate. It is used as submodule via git and it also contains a lot submodules for its modules and
+dependencies. So you should either clone this repository with `git clone --recurse-submodules` or 
+make sure to clone them in a later step manually.
+
+## Notes
+Be aware that those demo projects are built against the version of the VkCV framework which is
+used as submodule via git in this repository. So to be compatible with future versions of the
+framework some changes/adjustments might be required.