update supported Python version. I've been running w/ 3.10.

README.md

@@ -94,17 +94,17 @@ ntunnel quic_client --ca-certs funkthat.crt tcp:127.0.0.1:42720 udp:192.0.2.5:12
 Running Tests
 -------------
 
-Currently ntunnel requires Python 3.7 or later.  If the default
-virtualenv is not 3.7 or later, you can set the VIRTUALENV variable to specify
+Currently ntunnel requires Python 3.10 or later.  If the default
+virtualenv is not 3.10 or later, you can set the VIRTUALENV variable to specify
 which one to use, such as:
 ```
-make env VIRTUALENV=virtualenv-3.7
+make env VIRTUALENV=virtualenv-3.10
 ```
 
 If you want to use an alternate version of python, you can specify
 VIRTUALENVARGS, such as:
 ```
-make env VIRTUALENV=virtualenv-3.7 VIRTUALENVARGS="-p $(which pypy3)"
+make env VIRTUALENV=virtualenv-3.10 VIRTUALENVARGS="-p $(which pypy3)"
 ```
 
 Once you have the environment setup, you can source the development