README.md: fix typo; cited article is about 'git'.

Signed-off-by: Phil Hord <hordp@cisco.com>
[rlb@defaultvalue.org: adjust commit message.]
Reviewed-by: Rob Browning <rlb@defaultvalue.org>
Add /t/tmp/ to .gitignore.

Signed-off-by: Phil Hord <hordp@cisco.com>
Reviewed-by: Rob Browning <rlb@defaultvalue.org>