user-manual: Update download size for Git and the kernel

user-manual: Update download size for Git and the kernel

They've grown since d19fbc3 (Documentation: add git user's manual,
2007-01-07) when the stats were initially added.  I've rounded
download sizes up to the nearest multiple of ten MiB to decrease the
precision and give a bit of growing room.  Exact sizes:

  $ git clone git://git.kernel.org/pub/scm/git/git.git
  Initialized empty Git repository in /tmp/git/.git/
  remote: Counting objects: 156872, done.
  remote: Compressing objects: 100% (40826/40826), done.
  remote: Total 156872 (delta 115322), reused 155492 (delta 114094)
  Receiving objects: 100% (156872/156872), 37.29 MiB | 7.54 MiB/s, done.
  Resolving deltas: 100% (115322/115322), done.

  $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
  Initialized empty Git repository in /tmp/linux/.git/
  remote: Counting objects: 3057404, done.
  remote: Compressing objects: 100% (474769/474769), done.
  Receiving objects: 100% (3057404/3057404), 634.33 MiB | 27.95 MiB/s, done.
  remote: Total 3057404 (delta 2570385), reused 3040910 (delta 2554408)
  Resolving deltas: 100% (2570385/2570385), done.
  Checking out files: 100% (43012/43012), done.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>