nice formatting for ECDH example

tomato42 · tomato42 · commit 34864b1cb60d · 2019-11-30T16:34:59.000+01:00
colour the code in the ECDH example
diff --git a/README.md b/README.md
@@ -469,7 +469,7 @@ print(vk.to_string("uncompressed").hex())
 
 ECDH key exchange with remote party
 
-```
+```python
 from ecdsa import ECDH, NIST256p
 
 ecdh = ECDH(curve=NIST256p)
