Add username mapping for katie@chromium.org

BUG=none
NOTRY=true

Change-Id: I083a43ee047984b91f301334f8b2fdf0d975d82d
Reviewed-on: https://chromium-review.googlesource.com/753657
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514160}

docs/user_handle_mapping.md

@@ -55,6 +55,7 @@ For Chromium contributors that have different nicks on other domains.
 | jshin             | jshin           | jungshik        |
 | jww               | jww\_\_         | jww             |
 | jyasskin          | jyasskin        | jyasskin        |
+| katie             |                 | katydek         |
 | karen             | kareng          | kareng          |
 | keescook          | kees            | keescook        |
 | koz               |                 | jameskozianski  |