Add a .mailmap file

..so that `git shortlog --author=thakis` manages to print all my
commits as coming from the single person that I am most days.

Not sure where that weird @0039d316-1c4b-4281-b951-d872f2087c98
email address came from.

No behavior change to gn itself.

Change-Id: I7d20fb17925c57c8fa1c47ffa7e1dee70d69115f
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/12960
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>

.mailmap

diff --git a/.mailmap b/.mailmap
new file mode 100644
index 0000000..1161de6
--- /dev/null
+++ b/.mailmap
@@ -0,0 +1,20 @@
+# This file allows mapping several author and committer email addresses and
+# names to a single canonical one for `git shortlog`, `git log --author`,
+# or `git check-mailmap`.
+#
+# For example, if you commit as `random.person@example.com` but sometimes use
+# "Rañdom Person" and sometimes "Random Person" as name and you want the former
+# to be your canonical name, add
+#
+#     Rañdom Person <random.person@example.com>
+#
+# If you commit as both `random.person@example.com` and `ranp@example.com` and
+# you want the former to be your canonical email address, add
+#
+#     <random.person@example.com> <ranp@example.com>
+#
+# Combinations of both are possible too, see
+# https://git-scm.com/docs/gitmailmap for format details.
+
+Nico Weber <thakis@chromium.org>
+Nico Weber <thakis@chromium.org> <thakis@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>