[MonteCarlo Laser Loc] introduce several optimization techniques in the user doc

that can be used. For instance downsampling the laser readings (180 ---> 18?) and computing the theoretical laser readings raytracing on a smaller map image (1024x1024 -----> 400 x 400?).

Applying them the number of particles on real-time operation of the localization algorithm can be larger, and so the relocalization power of the MCL algorithm.