modified thread param description to explain how to get reproducible results (#634)

Summary:
Hi,
here is the second PR on the reproducible results 'how-to'.

As I said, feel free to choose which one to merge (or eventually to trash both of them).

Thanks!
Leonardo
Pull Request resolved: https://github.com/facebookresearch/fastText/pull/634

Reviewed By: EdouardGrave

Differential Revision: D14996871

Pulled By: Celebio

fbshipit-source-id: d55115fa55bf9dbab73c31794f4b52049c6e9a1c

src/args.cc

@@ -235,7 +235,7 @@ void Args::printTrainingHelp() {
       << "  -neg                number of negatives sampled [" << neg << "]\n"
       << "  -loss               loss function {ns, hs, softmax, one-vs-all} ["
       << lossToString(loss) << "]\n"
-      << "  -thread             number of threads [" << thread << "]\n"
+      << "  -thread             number of threads (set to 1 to ensure reproducible results) [" << thread << "]\n"
       << "  -pretrainedVectors  pretrained word vectors for supervised learning ["
       << pretrainedVectors << "]\n"
       << "  -saveOutput         whether output params should be saved ["