Add some METADATA files to control docs layout.

BUG=skia:3484
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=976303002

Review URL: https://codereview.chromium.org/976303002
diff --git a/site/METADATA b/site/METADATA
new file mode 100644
index 0000000..5c6310b
--- /dev/null
+++ b/site/METADATA
@@ -0,0 +1,4 @@
+{
+  "dirOrder": ["user", "dev"],
+  "fileOrder": []
+}