Updated readme (close #153); updated core

Author: TheMostDiligent

DiligentCore

@@ -323,6 +323,12 @@ cmake -S . -B ./build/MacOS -G "Xcode"
 
 The project will be located in `build/MacOS` folder.
 
+Note that if CMake fails to find the compiler, you may need to run the following command:
+
+```
+sudo xcode-select --reset
+```
+
 ### Configuring Vulkan Build Environment
 
 By default there is no Vulkan implementation on MacOS. Diligent Engine loads Vulkan dynamically
@@ -458,6 +464,9 @@ The diagram below shows the dependencies between modules.
    '----------------->Samples
 ```
 
+Don't forget to recursively initialize submodules if you are adding Diligent repos
+as submodules to your project.
+
 ### Your Project Uses Cmake
 
 If your project uses CMake, adding Diligent Engine requires just few lines of code. 

README.md

@@ -29,10 +29,15 @@ git submodule update --recursive
 * When building on Windows, generating Visual Studio project files is the recommended way.
   Other IDEs such as Visual Studio Code or CLion may need extra configuration to properly set up
   the build environment.
- 
+
 * If on Windows you get long path error, try cloning the project to a folder with shorter name
   such as `c:/git/DiligentEngine`.
 
+* If on MacOS CMake fails to find the compiler, run the following command:
+  ```cmake
+  sudo xcode-select --reset
+  ```  
+
 ### Projects don't run
 
 * When running from the command line, make sure that the project's `assets` folder is set as working directory