Add top-level README

docs/design/README.md

@@ -0,0 +1,16 @@
+# Design docs
+
+This directory contains design documentation for Tessera.
+
+It's probably wise to start with the [philosophy](philosophy.md]) doc first in order to provide
+the context around the approach and design trade-offs made herein.
+
+## Storage
+
+Tessera supports multiple backend storage implementations, each of these has an associated
+"one-pager" design doc:
+
+* [GCP](storage_gcp.md)
+* [MySQL](storage_mysql.md)
+* [POSIX filesystem](storage_posix.md)
+