gpu-dawn: initialize subrepository

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

gpu-dawn/.gitignore

@@ -0,0 +1,18 @@
+# This file is for zig-specific build artifacts.
+# If you have OS-specific or editor-specific files to ignore,
+# such as *.swp or .DS_Store, put those in your global
+# ~/.gitignore and put this in your ~/.gitconfig:
+#
+# [core]
+#     excludesfile = ~/.gitignore
+#
+# Cheers!
+# -andrewrk
+
+zig-cache/
+zig-out/
+/release/
+/debug/
+/build/
+/build-*/
+/docgen_tmp/