updated installation.md for arch based distributions.
updated installation.md for arch based distributions.

IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,floe/librealsense,IntelRealSense/librealsense,floe/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,floe/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense