docs: add proto crate README

Author: evansims

crates/proto/README.md

@@ -0,0 +1,30 @@
+# inferadb-ledger-proto
+
+Generated protobuf types, gRPC service traits, and domain type conversions for [InferaDB](https://github.com/inferadb) [Ledger](https://github.com/inferadb/ledger).
+
+## Overview
+
+This crate provides the wire-format layer for InferaDB Ledger:
+
+- **Proto types**: Generated request/response messages, enums, and nested types
+- **gRPC traits**: Service definitions for Read, Write, Admin, Health, and Discovery
+- **Conversions**: Bidirectional `From`/`TryFrom` impls between proto and domain types
+
+## Usage
+
+```rust
+use inferadb_ledger_proto::proto::{
+    WriteRequest, ReadRequest, Operation,
+    write_service_client::WriteServiceClient,
+    read_service_client::ReadServiceClient,
+};
+
+// Convert between domain and proto types
+use inferadb_ledger_types::Operation as DomainOp;
+let domain_op = DomainOp::set_entity("key", b"value".to_vec());
+let proto_op: Operation = domain_op.into();
+```
+
+## License
+
+MIT OR Apache-2.0