MacOS build instructions

[JeremyMain]

I was able to build this on MacOS as well and it would be good to add the following to the project readme

MacOS
in the project directory create a build directory and change into the directory, then run cmake and then make.

git clone --depth 1 https://github.com/Raais/ImStudio.git
cd ImStudio
mkdir build
cd build
cmake ..
make

The resulting ImStudio.app application will be found in

project-root/build/src/