Improve Description of `--blanks-separate-docs`.

[PhilipMay]

Hi. I do not fully understand the meaning of --blanks-separate-docs. I know that this is important for "next sentence prediction" with normal BERT. But I do not think that this is done at electra training. So my question is: How does this setting influence the training and the quality of the model? Or does it even influence the result at all?

Since I think that some other ppl. have the same question maybe this can also be a feature request for more documentation about this.

Many thanks Philip