Add short doc for cleandead tool, fix #1716
Add short doc for cleandead tool, fix #1716

maruel/ninja,iwadon/ninja,bradking/ninja,maruel/ninja,AoD314/ninja,iwadon/ninja,sgraham/ninja,sgraham/ninja,maruel/ninja,iwadon/ninja,sgraham/ninja,AoD314/ninja,Qix-/ninja,maruel/ninja,Qix-/ninja,bradking/ninja,sgraham/ninja,bradking/ninja,bradking/ninja,iwadon/ninja,ninja-build/ninja,ninja-build/ninja,AoD314/ninja,AoD314/ninja,ninja-build/ninja,Qix-/ninja,Qix-/ninja,ninja-build/ninja