Update packedGit config option documentation. Corrected minor typos and documented the new k/m/g suffix for core.packedGitWindowSize and core.packedGitLimit. [jc: with a minor markup fix.] Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>