update gstlal citation

Hi @brandon.piotrzkowski

Gstlal team has been writing two papers (one for MDC performance paper and one for method paper).
We would like to cite both papers for completeness, though they have not been submitted to Arxiv yet.

So I would like to ask following questions:

1. would it be okay to cite the two papers?
2. I think the both papers will be in arxiv and citable in a couple of weeks. Is that reasonable timeline? or too late?

Thanks!