Document a required dependency

README.md

@@ -24,6 +24,12 @@ The carrotcoin blockchain starts on December 20, 2025, at UTC 13:00. Before that
 
 ## Getting started
 
+Install one required dependency:
+
+```sh
+pip install cryptography
+```
+
 Run `./node.py` and pass any number of initial peer addresses as commandline arguments.
 
 There is one specific introducer node that you can use to connect your node to the network: