docs: add trezor signing to docs

docs/signing.rst

@@ -56,6 +56,15 @@ To sign, select an account in Frame and do this:
 
 Frame exposes an RPC connection at ``http://127.0.0.1:1248`` and exposes the currently selected account as ``eth_accounts[0]``. Ape Safe sends the payload as ``eth_signTypedData_v4``, which must be supported by your signer device.
 
+Trezor
+------
+
+Alternative method for Trezor models and firmware versions which don't support EIP-712 using ``eth_sign``:
+
+.. code-block:: python
+
+    >>> safe.sign_with_trezor(safe_tx)
+
 
 .. _`transaction service`: https://safe-transaction.gnosis.io/
 .. _`a delegate`: https://safe-transaction.gnosis.io/