update readme for firmware hash check (#50)

Author: 424778940z

README.md

@@ -37,6 +37,28 @@ OnekeyProBTFW_FACTORY_HEX
 OnekeyProBTFW_FLASH_FACTORY
 ```
 
+## How to verify firmware hash
+
+Install Python 3.x
+
+Download latest `ota.bin`, open a terminal in the same folder, invoke python, then run following code
+
+```python
+import struct, hashlib
+
+with open("ota.bin", mode="br") as f:
+    f.seek(0x0C)
+    codelen = struct.unpack("i", f.read(4))[0] - 512
+    f.seek(0x600)
+    print("".join(format(x, "02x") for x in hashlib.sha256(f.read(codelen)).digest()))
+```
+
+Single line version
+
+```python
+exec("""\nimport struct, hashlib\nwith open("ota.bin", mode="br") as f:\n    f.seek(0x0C)\n    codelen = struct.unpack("i", f.read(4))[0] - 512\n    f.seek(0x600)\n    print("".join(format(x, "02x") for x in hashlib.sha256(f.read(codelen)).digest()))\n""")
+```
+
 ## License
 
-Please check License.md for details
+Please check License.md for details