Mention the requirement of ninja-build as a dependency about raylib-rs

[jestarray]

https://github.com/Rover656/raylib-rs/blob/986141500cad72848b16f3e8c6f2780f74277da1/raylib-sys/build.rs#L62
Since this commit, windows builds will break without ninja being in PATH, as well as linux. It might be better if we remove .generator("Ninja") and not have to deal with this. Advanced users can edit and build with ninja as they'd like.

https://discord.com/channels/426912293134270465/540620507708522517/1138805729541763082
building on windows will error out

 --- stderr
  CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
    Compatibility with CMake < 3.5 will be removed from a future version of
    CMake.

    Update the VERSION argument <min> value or use a ...<max> suffix to tell
    CMake that the project does not need compatibility with older versions.


  CMake Error: CMake was unable to find a build program corresponding to "Ninja".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.
  thread 'main' panicked at '
  command did not execute successfully, got: exit code: 1

[jestarray]

Oh I mispoke, so this only seems to be a problem with the 4.0+ bindings: https://github.com/deltaphc/raylib-rs/tree/4.0.0
not the current master 3.7, but its something to keep in mind