mailmap: Add a few entries.
+Aman Agrawal <f2016561@pilani.bits-pilani.ac.in>
Anders Kaseorg <anders@zulip.com> <anders@zulipchat.com>
Anders Kaseorg <anders@zulip.com> <andersk@mit.edu>
Rishi Gupta <rishig@zulip.com> <rishig@zulipchat.com>
@@ -7,3 +8,4 @@ Steve Howell <showell@zulip.com> <steve@zulip.com>
Tim Abbott <tabbott@zulip.com> <tabbott@humbughq.com>
Tim Abbott <tabbott@zulip.com> <tabbott@mit.edu>
Tim Abbott <tabbott@zulip.com> <tabbott@zulipchat.com>
+Zixuan James Li <p359101898@gmail.com> <359101898@qq.com>
