Update confirmation email

[tiffanyqi]

Change to this:

Subject: [CSM] Email Confirmation Instructions

Welcome to CSM's scheduling service!
Please confirm your account to get started. You can confirm your account email through the link below:
Confirm my account

Let us know if you have any questions.
Best,
CSM

[Zhangerr]

The file in question for confirmation emails is here:
app/views/devise/mailer/confirmation_instructions.html.erb

I'm not sure where to actually change the subject, though. Maybe it's a setting for devise? Or do we have to overwrite it?