README: Revise adding aptitude examples

Signed-off-by: Toni Gundogdu <legatvs@gmail.com>
Workaround: AM_PROG_AR

Signed-off-by: Toni Gundogdu <legatvs@gmail.com>
Add config.aux/ar-lib to .gitignore

Signed-off-by: Toni Gundogdu <legatvs@gmail.com>