Add docs/external_resources.md to put links to google docs etc.

Bug: dawn:773
Change-Id: I52f405a8edf6c15067bbf51a547a9eedbf72f9e8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/60162
Reviewed-by: Shrek Shao <shrekshao@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Shrek Shao <shrekshao@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
Auto-Submit: Shrek Shao <shrekshao@google.com>
diff --git a/docs/external_resources.md b/docs/external_resources.md
new file mode 100644
index 0000000..91f7a60
--- /dev/null
+++ b/docs/external_resources.md
@@ -0,0 +1,6 @@
+# Dawn's external resources links
+
+## Design Docs
+
+- Buffer mapping dawn wire memory transfer interface design
+    - https://docs.google.com/document/d/1JOhCpmJ_JyNZJtX6MVbSgxjtG1TdKORdeOGYtSfVYjk/edit?usp=sharing&resourcekey=0-1bFi47mR1jkBLdRFxcTVig
\ No newline at end of file