Improve on-boarding mail with recovery

[webwizart]

The recovery email is confusing it speaks about 3 things you need to handle your account and that’s not clear.

• Magic Recovery Code,
• Password,
• Secret Recovery Key.

We should add some explanation in the email for each part of the recovery. Or at least add a link to the documentation.

https://docs.blockstack.org/browser/ids-introduction.html