[Quick fix] Make checkpointing optional in example

[yhn112]

No description provided.

[codecov]

Codecov Report

Merging #303 (818aa89) into master (e9956b8) will decrease coverage by 0.34%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #303      +/-   ##
==========================================
- Coverage   81.86%   81.52%   -0.35%     
==========================================
  Files          63       63              
  Lines        5813     5813              
==========================================
- Hits         4759     4739      -20     
- Misses       1054     1074      +20     

Impacted Files	Coverage Δ
hivemind/client/averaging/matchmaking.py	77.53% <0.00%> (-5.85%)	⬇️
hivemind/client/averaging/key_manager.py	95.45% <0.00%> (-2.28%)	⬇️
hivemind/p2p/p2p_daemon.py	90.49% <0.00%> (-1.15%)	⬇️
hivemind/utils/timed_storage.py	95.91% <0.00%> (-1.03%)	⬇️
hivemind/dht/protocol.py	93.36% <0.00%> (-0.42%)	⬇️
hivemind/utils/mpfuture.py	95.38% <0.00%> (+0.76%)	⬆️
hivemind/dht/node.py	93.23% <0.00%> (+1.25%)	⬆️