Add a freetype_update WATCHLIST entry to monitor FreeType rolls

Intended to help synchronizing FreeType version between Chromium and PDFium.

Tested using
$ ../../depot_tools/watchlists.py third_party/freetype/README.chromium
['thestig@chromium.org', 'drott+watch@chromium.org']

Tbr: thestig, bungeman
Change-Id: I60d4ebfac716a3625b8d6698bf181b971b091eeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660663Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669616}

WATCHLISTS

@@ -946,6 +946,9 @@
                   'google_apis/drive|' \
                   'ui/file_manager'
     },
+    'freetype_update': {
+      'filepath': 'third_party/freetype/README.chromium',
+    },
     'fsp': {
       'filepath': 'chrome/browser/chromeos/extensions/file_system_provider|' \
                   'chrome/browser/chromeos/file_system_provider|' \
@@ -2312,6 +2315,8 @@
     'filesapp': ['filesapp-reviews@chromium.org',
                  'fukino+watch@chromium.org',
                  'yamaguchi+watch@chromium.org'],
+    'freetype_update': ['drott+watch@chromium.org',
+                        'thestig@chromium.org'],
     'fsp': ['mtomasz+watch@chromium.org'],
     'fuchsia': ['sergeyu@chromium.org', 'wez@chromium.org'],
     'fuzzing': ['fuzzing@chromium.org'],