Should clarify that the `setup-env` script is linux only.

[charles-lunarg]

Vulkan-Tutorial/en/02_Development_environment.adoc

Line 68 in b65ff32

To automatically set the environment variables up that VulkanSDK will use to

This block of text is linux specific (windows SDK installer sets up the env-vars automatically, macOS has different patterns but also has an installer).

[SaschaWillems]

Fixed via #176