On forgot password page, suggest that users check which city they're in

[misaugstad]

Brief description of problem/feature

Since we still don't have uniform login across cities (#1381), most of the complaints about not being able to login or reset passwords has to do with users expecting their logins to transfer between cities.

We could dispel some confusion by suggesting that as a potential issue on the Forgot Password page. And we could explain that they'd need to make an account in each city, so they should try that.

We could theoretically create an API endpoint to check if a user exists so that we can ping the other cities' servers to list which cities they have logins for... But I'm just assuming that that's bad practice as far as security goes.