Update 01-introduction.md

Fixed typo and included a description of Gemfile.lock.

Although Gemfile.lock isn't in the file system of a clean install of Padrino it will be there if someone is following along with the tutorial so I think the description should be there.
Merge pull request #27 from scottharvey/patch-1

Update 01-introduction.md
Add Scott to the list of contributors
Split the first chapter in smaller files
Fixed issue #5 - thanks to @rosstimson for providing the 
feedback