added ATL
updated readme to reflect new application settings

- closes #14
additional timezones
Update README.md

Add required libraries to installation instructions.
dd# Untracked files:
Updated time zones and email debugs
Update README.md

Corrected spelling
PS on line 50 - there is not a spot to edit the email and password in sw_checkin_email.py. SHould that be edit default_settings.py ?
Update README.md

Moved install notes for Ubuntu 12 to bottom
Added note about Gmail two factor auth.
fixes #19
readme clarification
send email if either config email option is set
Added MAX_RETRIES parameter.

When CHECKIN_WINDOW=0, the program gives up too early. Fixed this by adding a
MAX_RETRIES parameter instead.