Add helper page around account linking and multiple emails

Signed-off-by: Kai Wagner <kai.wagner@percona.com>

Author: ImTheKai

app/controllers/help_controller.rb

@@ -4,7 +4,8 @@ class HelpController < ApplicationController
   layout "help"
 
   PAGES = {
-    "hackorum-patch" => "Applying Patches with hackorum-patch"
+    "hackorum-patch" => "Applying Patches with hackorum-patch",
+    "account-linking" => "Account Linking & Multiple Emails"
   }.freeze
 
   def index

app/views/help/pages/account-linking.md

@@ -0,0 +1,29 @@
+# Account Linking & Multiple Emails
+
+If you use different email addresses on different devices (for example, a work address on your work laptop and a personal address on your phone), you can still use a single Hackorum account. Below are two supported ways to do that.
+
+## Option A: Connect a Google account
+
+Use this when you want to sign in with Google on one device and keep using your existing Hackorum account.
+
+1. Go to **Settings → Account & Emails**.
+2. In **Connected accounts**, click **Connect Google account** and complete the Google OAuth flow.
+3. The Google identity will appear in the **Connected accounts** list.
+
+## Option B: Add a second email and set a password
+
+Use this when you want to sign in with multiple email addresses (not only Google).
+
+1. Go to **Settings → Password** and set a password (you can also change it if you already have one and cannot remember).
+2. Go to **Settings → Account & Emails**.
+3. Under **Email addresses**, add your second email and click **Send verification**.
+4. Verify the email via the link you receive.
+5. You can now sign in with either email address using the same password.
+
+These options keep everything in one account while letting you use whichever email is most convenient on each device.
+
+## Mailing list addresses
+
+If you have posted to the mailing list from multiple addresses over the years, add those addresses to your Hackorum account too. This ensures all of your past and future posts appear under one user account, no matter which email you used at the time.
+
+If you no longer have access to an old address (and cannot verify it), contact an administrator. They can add it to your account from the backend.