Add .mailmap

Before:

  codemirror-editor $ git shortlog -n -s
      22  Kasper Nilsson
      16  Paladox none
       2  Viktar Donich
       1  Dave Borowitz
       1  David Ostrovsky
       1  brohlfs

After:

  codemirror-editor $ git shortlog -n -s
      22  Kasper Nilsson
      16  Paladox none
       2  Viktar Donich
       1  Ben Rohlfs
       1  Dave Borowitz
       1  David Ostrovsky

Change-Id: Ib1681e1ff4a6a2eb9849313b4dbd194b75d84ebd
diff --git a/.mailmap b/.mailmap
new file mode 100644
index 0000000..7217c82
--- /dev/null
+++ b/.mailmap
@@ -0,0 +1 @@
+Ben Rohlfs <brohlfs@google.com> brohlfs <brohlfs@google.com>
\ No newline at end of file