mailmap: add .peoplemap

In .mailmap, an individual may be represented by multiple mails which
may reflect an organization affiliation change that needs to be
preserved to find out which organization sponsored which commit.

The .peoplemap file aggregates these mails to show a single line for
each person

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #2366 from dachary/wip-mailmap

mailmap: add .peoplemap

Reviewed-by: M Ranga Swami Reddy <swamireddy@gmail.com>