Add re-thread to External Resources doc
Add re-thread to External Resources doc

As requested, added [re-thread](https://github.com/yetanalytics/re-thread).
Day8/re-frame,daiyi/re-frame,chpill/re-frankenstein,martinklepsch/re-frame,richardharrington/re-frame,Day8/re-frame,daiyi/re-frame,chpill/re-frankenstein,martinklepsch/re-frame,daiyi/re-frame,chpill/re-frankenstein,richardharrington/re-frame,Day8/re-frame,martinklepsch/re-frame,richardharrington/re-frame