Update documentation for Covariance
Update documentation for Covariance

Change-Id: Ia4a7347ef8267b7107698d85fcbfc986111958dc

ikoruk/ceres-solver,stonier/ceres_solver,entylop/ceres-solver,kartikkumar/ceres-solver,stonier/ceres_solver,kartikkumar/ceres-solver,timfel/ceres-bin,stonier/ceres_solver,jmwalls/ceres-solver-fork,ikoruk/ceres-solver,timfel/ceres-bin,jmwalls/ceres-solver-fork,ysonggit/ceres-solver,timfel/ceres-bin,ysonggit/ceres-solver,entylop/ceres-solver,ikoruk/ceres-solver,kartikkumar/ceres-solver,ikoruk/ceres-solver,whuaegeanse/ceres-solver,DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,ysonggit/ceres-solver,jmwalls/ceres-solver-fork,entylop/ceres-solver,jmwalls/ceres-solver-fork,whuaegeanse/ceres-solver,whuaegeanse/ceres-solver,entylop/ceres-solver,DougFirErickson/ceres-solver,ysonggit/ceres-solver,DougFirErickson/ceres-solver,DougFirErickson/ceres-solver,timfel/ceres-bin,stonier/ceres_solver,ikoruk/ceres-solver,kartikkumar/ceres-solver