[alaveteli/6169] Create a /help page regarding account security / two factor authentication

[mdeuk]

We should create a page in /help that provides users with information about how to keep their account safe, and how to use two factor / multi factor authentication.

I'm splitting this off from the master ticket so we can look at any WDTK specific scenario.

@MattK1234 wrote in mysociety/alaveteli#6169:

We don't ask for the two factor passcode particularly often. Occasionally the WDTK team receive some correspondence from users who might have forgotten about this.

As 2FA can take many forms some users are expecting a text message or email address or some other form of communication.

We could provide some additional information here to help users understand what we are asking for, maybe by a little question mark of help icon displaying the some text or similar.

We could also highlight our inability to do anything if the OTP is forgotten.

Is it really a one-time passcode though? Surely it would be used every time a user changes their password? We might want to consider changing that terminology.

[HelenWDTK]

+1 We've had a few cases recently where users have seemed confused about two factor authentication

[HelenWDTK]

This might be worth picking up, as we've had a few of these recently.