Make Vulkan requirement an important note in Compiling for macOS (#4545)

Co-authored-by: Hugo Locurcio <[email protected]>

development/compiling/compiling_for_osx.rst

@@ -16,8 +16,10 @@ For compiling under macOS, the following is required:
   (or the more lightweight Command Line Tools for Xcode).
 - *Optional* - `yasm <https://yasm.tortall.net/>`_ (for WebM SIMD optimizations).
 
-If you are building the ``master`` branch:
-- Download and install the `Vulkan SDK for macOS <https://vulkan.lunarg.com/sdk/home>`__.
+.. important::
+
+    If you are building the ``master`` branch, download and install the
+    `Vulkan SDK for macOS <https://vulkan.lunarg.com/sdk/home>`__.
 
 .. note:: If you have `Homebrew <https://brew.sh/>`_ installed, you can easily
           install SCons and yasm using the following command::