[SP] Add comment in .idl to avoid build warning.
[SP] Add comment in .idl to avoid build warning.

Build warning:
"
ninja: Entering directory `out\Release_x64'
[195/337] ACTION //extensions/realsense/scene_perception/win:scene_perception_idl_gen(//build/toolchain/win:64)
scene_perception must have a namespace-level comment. This will appear on the API summary page.
"

jondong/realsense-extensions-crosswalk,halton/realsense-extensions-crosswalk,crosswalk-project/realsense-extensions-crosswalk,crosswalk-project/realsense-extensions-crosswalk,halton/realsense-extensions-crosswalk,crosswalk-project/realsense-extensions-crosswalk,jondong/realsense-extensions-crosswalk,halton/realsense-extensions-crosswalk,halton/realsense-extensions-crosswalk,crosswalk-project/realsense-extensions-crosswalk,jondong/realsense-extensions-crosswalk,jondong/realsense-extensions-crosswalk