miden-tx: add readme (#503)

miden-tx/README.md

@@ -0,0 +1,49 @@
+# Miden Transaction
+
+This crate contains tools to create, execute, and prove transactions.
+
+## Usage
+
+This crate exposes a few components to compile, run, and prove transactions.
+
+The first requirement is to have a `DataStore` implementation. `DataStore`
+objects are responsible to load the data needed by the transactions executor,
+specially the account's code, the reference block data, and the note's inputs.
+
+```rust
+let store = DataStore:new();
+```
+
+Once a store is available, a `TransactionExecutor` object can be used to
+execute a transaction. Consuming a zero or more notes, and possibly calling
+some of the account's code.
+
+```rust
+let executor = TransactionExecutor::new(store);
+let executed_transaction = executor.execute_transaction(account_id, block_ref, note_ids, tx_args);
+```
+
+With the transaction execution done, it is then possible to create a proof:
+
+```rust
+let prover = TransactionProver::new(ProvingOptions::default());
+let proven_transaction = prover.prove_transaction(executed_transaction);
+```
+
+And to verify a proof:
+
+```rust
+let verifier = TransactionVerifier::new(SECURITY_LEVEL);
+verifier.verify(proven_transaction);
+```
+
+## Features
+
+| Features     | Description                                                                                   |
+| ------------ | --------------------------------------------------------------------------------------------- |
+| `std`        | Enable usage of Rust's `std`, use `--no-default-features` for `no-std` support.               |
+| `concurrent` | Enables concurrent code to speed up runtime execution.                                        |
+
+## License
+
+This project is [MIT licensed](../LICENSE).