Merge branch 'readme' into 'master'

Update CMake instructions

See merge request jvet/VVCSoftware_VTM!894

README.md

@@ -21,20 +21,38 @@ mkdir build
 Use one of the following CMake commands, based on your platform. Feel free to change the commands to satisfy
 your needs.
 
-**Windows Visual Studio 2015 64 Bit:**
+**Windows Visual Studio 2015/17/19 64 Bit:**
+
+Use the proper generator string for generating Visual Studio files, e.g. for VS 2015:
+
 ```bash
 cd build
 cmake .. -G "Visual Studio 14 2015 Win64"
 ```
+
 Then open the generated solution file in MS Visual Studio.
 
+For VS 2017 use "Visual Studio 15 2017 Win64", for VS 2019 use "Visual Studio 16 2019".
+
+Visual Studio 2019 also allows you to open the CMake directory directly. Choose "File->Open->CMake" for this option.
+
 **macOS Xcode:**
+
+For generating an Xcode workspace type:
 ```bash
 cd build
 cmake .. -G "Xcode"
 ```
 Then open the generated work space in Xcode.
 
+For generating Makefiles with optional non-default compilers, use the following commands:
+
+```bash
+cd build
+cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER=gcc-9 -DCMAKE_CXX_COMPILER=g++-9
+```
+In this example the brew installed GCC 9 is used for a release build.
+
 **Linux**
 
 For generating Linux Release Makefile: