Add transaction builder with metadata example (#327)

* Add transaction builder example with metadata

* Add transaction builder example with metadata

* Add CIP-20 metadata example

* Reformat file

Author: B3nac

examples/tx_builder_with_metadata.py

@@ -0,0 +1,56 @@
+from blockfrost import ApiUrls
+
+from pycardano import (
+    Address,
+    AlonzoMetadata,
+    AuxiliaryData,
+    BlockFrostChainContext,
+    Metadata,
+    Network,
+    PaymentSigningKey,
+    PaymentVerificationKey,
+    TransactionBuilder,
+    TransactionOutput,
+)
+
+# Use testnet
+network = Network.TESTNET
+
+# Read keys to memory
+# Assume there is a payment.skey file sitting in current directory
+payment_signing_key = PaymentSigningKey.load("payment.skey")
+payment_verification_key = PaymentVerificationKey.from_signing_key(payment_signing_key)
+
+from_address = Address(payment_verification_key.hash(), network=network)
+
+# Create a BlockFrost chain context. In this example, we will use preprod network.
+context = BlockFrostChainContext(
+    "your_blockfrost_project_id", base_url=ApiUrls.preprod.value
+)
+
+# Metadata that follows the CIP-20 standard. More info here https://cips.cardano.org/cip/CIP-20/
+metadata = {
+    674: {
+        "msg": [
+            "Invoice-No: 1234567890",
+            "Customer-No: 555-1234",
+            "P.S.: i will shop again at your store :-)",
+        ]
+    }
+}
+
+# Place metadata in AuxiliaryData, the format acceptable by a transaction.
+auxiliary_data = AuxiliaryData(AlonzoMetadata(metadata=Metadata(metadata)))
+# Set transaction metadata
+builder.auxiliary_data = auxiliary_data
+# Create a transaction builder
+builder = TransactionBuilder(context)
+# Set your address
+builder.add_input_address(from_address)
+# Recipient address
+to_address = "cardano_address_you_want_to_send_ada_to"
+# Add output and sign transaction
+builder.add_output(TransactionOutput.from_primitive([to_address, 100000000000]))
+signed_tx = builder.build_and_sign([payment_signing_key], change_address=from_address)
+# Send transaction
+context.submit_tx(signed_tx)