Update third_party/freetype/README.pdfium.

- Add a FreeType bug URL for more context on the local FreeType
  modification.
- Fix a typo.

Change-Id: I773559d78ba0b73988d57a54a17c69645df8d77d
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/90310
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/third_party/freetype/README.pdfium b/third_party/freetype/README.pdfium
index 4df4867..9a4ebf6 100644
--- a/third_party/freetype/README.pdfium
+++ b/third_party/freetype/README.pdfium
@@ -14,7 +14,9 @@
 
 include/pstables.h: A copy of freetype/src/psnames/pstables.h.  This file is not
 part of the public Freetype API, but pdfium needs it.  Since it won't be
-avilable when building with the system Freetype, we provide it as a convenience.
+available when building with the system Freetype, we provide it as a
+convenience. See https://gitlab.freedesktop.org/freetype/freetype/-/issues/731
+for the request to make this a public Freetype API.
 
 0000-include.patch: Modifications to configuration header files.