docs: add remaining docs for classes in app/logical.

app/mailers/user_mailer.rb

@@ -2,21 +2,25 @@ class UserMailer < ApplicationMailer
   helper :application
   helper :users
 
+  # The email sent when a user receives a DMail.
   def dmail_notice(dmail)
     @dmail = dmail
     mail to: dmail.to.email_with_name, subject: "#{Danbooru.config.app_name} - Message received from #{dmail.from.name}"
   end
 
+  # The email sent when a user requests a password reset.
   def password_reset(user)
     @user = user
     mail to: @user.email_with_name, subject: "#{Danbooru.config.app_name} password reset request"
   end
 
+  # The email sent when a user changes their email address.
   def email_change_confirmation(user)
     @user = user
     mail to: @user.email_with_name, subject: "Confirm your email address"
   end
 
+  # The email sent when a new user signs up with an email address.
   def welcome_user(user)
     @user = user
     mail to: @user.email_with_name, subject: "Welcome to #{Danbooru.config.app_name}! Confirm your email address"