[enh] tx example: create key earlier in order to gather pubkey rather than asking for it.

examples/send_transaction.py

@@ -96,8 +96,9 @@ async def main():
     # prompt hidden user entry
     password = getpass.getpass("Enter your password: ")
 
-    # prompt entry
-    pubkey_from = input("Enter your pubkey: ")
+    # create keys from credentials
+    key = SigningKey.from_credentials(salt, password)
+    pubkey_from = key.pubkey
 
     # prompt entry
     pubkey_to = input("Enter recipient pubkey: ")
@@ -118,9 +119,6 @@ async def main():
     # create the transaction document
     transaction = get_transaction_document(current_block, source, pubkey_from, pubkey_to)
 
-    # create keys from credentials
-    key = SigningKey.from_credentials(salt, password)
-
     # sign document
     transaction.sign([key])