Use offset to specify Bitcoin Basic HTLC Swap

[D4nte]

Use the following text:

** Bitcoin on Bitcoin **
Contract template:
 6382012088a82010000000000000000000000000000000000000000000000000000000000000018876a9143000000000000000000000000000000000000003670420000002b17576a91440000000000000000000000000000000000000046888ac
| Name | Byte Range | Length (bytes) |
|:--- |:--- |:--- |
| `secret_hash` | 7..39 | 32 |
| `redeem_identity` | 43..63 | 20 |
| `refund_timestamp` | 65..69 | 4 |
| `refund_identity` | 74..94 | 20 |