doc: Add "Pending" string back in for shader checker
doc: Add "Pending" string back in for shader checker

"Pending" is used as a trigger keyword for document validator to know
when one section is ending and a new section is starting so adding it
back in to get doc validation passing.

Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,Radamanthe/VulkanSamples