Update hacker-guide.md
Update hacker-guide.md

Added two more Git learning resources
boldradius/scala-lang,boldradius/scala-lang,andy1138/scala-lang,jeantil/scala-lang,jeantil/scala-lang,boldradius/scala-lang,jeantil/scala-lang,andy1138/scala-lang,boldradius/scala-lang,andy1138/scala-lang,andy1138/scala-lang,vl4ds/scala-lang,jeantil/scala-lang,vl4ds/scala-lang,vl4ds/scala-lang,vl4ds/scala-lang