raposza/tools: platform/README.md

<!-- Copyright (c) 2026 bentzn --> <!-- SPDX-License-Identifier: Apache-2.0 --> # Platform Shared modules, released together under one version. ## Boundary rule S-1 Vendor SDK types - Canton, Daml-LF, protobuf and gRPC - are confined to the modules whose job is translating between a vendor API and t