Add an FAQ about changing a recurration donation

Sometimes donors email us asking how to change their recurring donation. The functionality to do so is accessible at https://www.djangoproject.com/fundraising/manage-donations/ `` / but sometimes donors don't save the email with their ID. We need a form that donors can input their email address and have their ID mailed to them. Then we'll need some FAQ text for https://www.djangoproject.com/foundation/donate/.

Start by reviewing the existing donation-management flow at https://www.djangoproject.com/fundraising/manage-donations/ and the donation page at https://www.djangoproject.com/foundation/donate/. Determine how a donor ID is retrieved and emailed when given an email address, then add FAQ text explaining how to change a recurring donation. Done means the recovery form works and the FAQ is published.

Written by the indexing model from the issue text.