Remove date conversion and update readme

Not sure if it's a unix vs windows thing, but the add_date was not parsing correctly when I imported to Evernote (reverting to epoch for all bookmarks).

I'm on a mac and it works really well without the seconds conversion for me.

Also, I updated the readme to include the very handy explicit instructions in the bottom comment of your blogpost (at time of writing).

Thanks for writing the post - I would not have found it otherwise!