message: Docs: add Python examples for keypair generation
diff: -Sending transactions with Python library
  +Sending Transactions With Python library
  ========================================
  Prerequisites
  -------------
  -.. note:: The library only works in Python 3 environment (Python 2 is not supported yet).
  +.. note:: The library only works in Python 3 environment (Python 2 is not supported).
  To use Iroha Python library, you need to get it from the
  `repository <https://github.com/hyperledger/iroha-python>`_ or via pip3:
  @@ -13,7 +13,47 @@ To use Iroha Python library, you need to get it from the
  pip3 install iroha
  -Now, as we have the library, we can start sending the actual transactions.
  +Creating your own key pairs with Python library
  +-----------------------------------------------
  +
  +For testing purposes, you can use example keys.
  +But you can also create your own.
  +To create **native Iroha ed25519 SHA-3** keys (difference between algorithms can be found `here <../develop/keys.html>`__), please use the following code:
  +
  +.. code-block:: python
  +
  + from iroha import IrohaCrypto
  +
  + # these first two lines are enough to create the keys
  + private_key = IrohaCrypto.private_key()
  + public_key = IrohaCrypto.derive_public_key(private_key)
  +
  + # the rest of the code writes them into the file
  + with open('keypair.priv', 'wb') as f:
  + f.write(private_key)
  +
  + with open('keypair.pub', 'wb') as f:
  + f.write(public_key)
  +
  +And for HL Ursa ed25519 SHA-2 keys in Multihash format, please use:
  +
  +.. code-block:: python
  +
  + from iroha import IrohaCrypto, ed25519_sha2
  + from nacl.encoding import HexEncoder
  +
  + private_key = ed25519_sha2.SigningKey.generate()
  + public_key = IrohaCrypto.derive_public_key(private_key).encode('ascii')
  +
  + with open('keypair.priv', 'wb') as f:
  + f.write(private_key.encode(encoder=HexEncoder))
  + f.write(public_key[6:])
  +
  + with open('keypair.pub', 'wb') as f:
  + f.write(public_key)
  +
  +
  +Now, as we have the library and the keys, we can start sending the actual transactions.
  Running example transactions
  ----------------------------
  