Define native Android architecture and parity contract (#88)

README.md

@@ -75,6 +75,11 @@ Rollback-safe remove, move, and copy transactions, destination rules, and
 selective subtree reencryption are documented in
 [`docs/tree-mutations.md`](docs/tree-mutations.md).
 
+The native Android architecture, support policy and complete mobile parity/issue
+map are recorded in [`docs/android/architecture.md`](docs/android/architecture.md)
+and [`docs/android/parity.md`](docs/android/parity.md). Android implementation
+belongs to milestone 06; the decision record does not claim a shipped client.
+
 ## Project layout
 
 ```text