Property of GLAD_INCLUDE_DIRS is private
Since I wanted to use glad as subporject of my project, I wrote this code
```cmake
add_subdirectory(extern/glad) 
...
target_link_libraries(${PROJECT_NAME}
  OpenGL::GL
  glfw
  glad
...
```
However, *GLAD_INCLUDE_DIRS* of *glad* target is set to PRIVATE so that my compiler couldn't find *glad/glad.h*. After change property from PRIVATE to PUBLIC the problem resolved.

I just wonder why *GLAD_INCLUDE_DIRS* is set to private
Is there any reason for this?
https://github.com/Dav1dde/glad/blob/ec01ac515dba0730dca375887bb1bd60bc92013c/CMakeLists.txt#L84
To use *glad* target in other cmake project, I think *GLAD_INCLUDE_DIRS* should be set to PUBLIC not PRIVATE.