Update limitations
Update limitations

I have now tested with various test commands other than rpc-tests.py based, e.g.

- `bisect.sh 3 300 src/test/test_bitcoin` (automatically parallelized)
- `bisect.sh 3 300 "gtest-parallel-bitcoin -w 3 --print_test_times src/test/test_bitcoin"` (parallelized 'manually' with less cores)
- `bisect.sh 3 300 /bin/true` (dummy test, accepted as passed, exit code 0)
- `bisect.sh 3 300 /bin/false` (dummy test, declared as failed on first iteration, exit code 1)



Bitcoin-com/BUcash,Justaphf/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,BTCfork/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,Bitcoin-com/BUcash,Bitcoin-com/BUcash,BitcoinUnlimited/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Bitcoin-com/BUcash,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,Bitcoin-com/BUcash