Fix references to images in proposal documents #925

Job	Run time
Run Vulkan CTS framework tests to validate against XML changes	1m 59s
Verify repository license compliance	41s
Build the core-only spec, to try and catch ifdef errors in extension markup	53s
Build the vulkan specification and generate any associated files (such as vulkan.h)	7m 2s
Build a test spec and check against expectation, to make sure the spec toolchain works as expected	1m 20s
Run various checker scripts on the spec and XML sources	51s
Compile a simple test program that uses vulkan.h	9s
Generate the vulkan C++ header (vulkan.hpp)	1m 12s
Generate Rust bindings (Ash crate)	33s
Build-test Rust bindings (Ash crate)	41s
Compile a simple test program that uses vulkan.hpp	17s
	15m 38s

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