Update README with basic installation instructions
Cleanup purchase order view

This commit cleans up the purchase order view code, adding an HTML5
style placeholder for the date field and removing an unecessary p tag.
Add migration to create SpreePurchaseOrder

This commit adds the migration that creates the Spree Purchase Order
table where payment information is stored
Re-style admin source_view layout

This commit restyles the admin source_view layout and updates the en.yml
file with a missing translation