Add chapter on synchronization

[SaschaWillems]

Covers: Memory barriers, Execution barriers, Events, Changes in Sync2. Timeline Semaphores. "when to use X primitive". Difference between memory & image barriers.

Basic use cases for each.

Why sync is so explicit in Vulkan - reference opengl & why its good vulkan requires explicit sync.
How GPU sync differs from CPU sync. (The hardware differences essentially). Task vs Data parallelism.

Memory model - don't need to mention it.

Reference/Link to external articles & blogs that go into more detail.
vulkan-guide chapter:
https://github.com/KhronosGroup/Vulkan-Guide/blob/master/chapters/synchronization.adoc

Note: Copied from the old repo's project board