Light editing and punctuation fixes in chapter 01

I  made some changes to chapter 01-Introduction that I thought improved readability. Also, fixed some punctuation (e.g., changing "e.g" to "e.g.,"). I also added "serial commas" to lists (e.g., "User, Photo, or Todo note" vs. "User, Photo or Todo note". This difference though may be a cultural one, apparently (according to Wikipedia) it is fairly standard in US English to use a comma before the last list item but common in UK English to leave it out.

Hope this is helpful!

Marc