docs: update the gmail notification service to reflect the correct co…

docs/services/email.md

@@ -12,6 +12,19 @@ The Email notification service sends email notifications using SMTP protocol and
 * `html` - optional bool, true or false
 * `insecure_skip_verify` - optional bool, true or false
 
+### Using Gmail
+
+When configuring Gmail as the SMTP service:
+
+* `username` - Must be your Gmail address.
+* `password` - Use an App Password, not your regular Gmail password.
+
+To Generate an app password, follow this link https://myaccount.google.com/apppasswords
+
+!!! note
+    This applies to personal Gmail accounts (non-Google Workspace). For Google Workspace users, SMTP settings 
+    and authentication methods may differ.
+
 ## Example
 
 The following snippet contains sample Gmail service configuration:
@@ -23,11 +36,11 @@ metadata:
   name: argocd-notifications-cm
 data:
   service.email.gmail: |
-    username: $email-username
-    password: $email-password
+    username: $username
+    password: $password
     host: smtp.gmail.com
     port: 465
-    from: $email-username
+    from: $email-address
 ```
 
 Without authentication:
@@ -41,7 +54,7 @@ data:
   service.email.example: |
     host: smtp.example.com
     port: 587
-    from: $email-username
+    from: $email-address
 ```
 
 ## Template