docs: Update Vulkan config comments

Author: Eiton

src/resources/defaultConfig.ini

@@ -253,11 +253,13 @@ EnableModelShadow = 1
 ; More error info will be printed but it will impact performance.
 ; Vulkan SDK is required for printing Vulkan Validation error in Vulkan mode
 RendererDebugMode = 0
+; Vulkan mode only
 ; Maximum image size (in KB) that will be suballocated from a shared memory pool
 ; instead of receiving a dedicated allocation. Set to 0 to disable suballocation.
 ; Smaller values reduce memory overhead but may not pool many textures.
 ; Larger values pool more textures but may waste memory in partially-filled blocks.
 ImageSuballocThresholdKB = 1024
+; Vulkan mode only
 ; Size (in MB) of each memory block in the suballocation pool.
 ; Smaller blocks reduce waste for sparse workloads; larger blocks reduce allocation calls.
 ; Automatically capped to 25% of the GPU's device-local memory heap.