Add dna replication notes
Modify DNAReplication.md
Add open problems
Add open problems of Week 2 (How do we sequence antibiotics?)
Add hidden message
Add word count context example in
Update WordCount.context.md
Update WordCount.context.md
Add dev meetup for spark internal
Update the resources of Apache Spark related.

Add important papers, book, blogs, sites, and Weibos.
Update Overview.md for the scala resources
Update Overview.md for the spark internal video
Change the papers to the local files
Add the spark paper published on hotcloud 2010.
Add plan to Overview.md
start to learn actor model
Understand spark with a spark example
	new file:   3.Glance.with.debug.md
	new file:   img/mindmap/newOrUsedStage.jpg
	new file:   img/mindmap/wordcount.jpg
Add SparkContext flow
Add scheduler picture in
Draft.