Touchup edits to Overview section. Fix workshop dates.
Various touchup and clarification edits for section 2.
Mostly small edits to section 3.

I also added a few motivation quotes from my own notes.
Merge pull request #1 from hlapp/master

Various small changes
Merge pull request #2 from hlapp/hl-edits-1

Edits for Overview section.
Merge pull request #3 from hlapp/hl-edits-2

Edits for the Data Carpentry Workshops section (section 2)
Merge pull request #4 from hlapp/hl-edits-3

Edits for Section 3, Overview and interest in the first Data Carpentry workshop
small updates to registration section