docs: Add Email Notifications info (#9930)

* Add Email Notifications info

* remove spaces

* Add ` ` to smtp link

* Small fixes

* PR feedback

* npm run format:fix

* PR feedback

* update docs

* formatting

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Co-authored-by: Alex <alex.tran1502@gmail.com>

docs/docs/guides/smtp-gmail.md

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+# SMTP settings using Gmail
+
+This guide walks you through how to get the information you need to set up your Immich instance to send emails using Gmail's SMTP server.
+
+## Create an app password
+
+From your Google account settings
+
+- Add [2-Step Verification](https://support.google.com/accounts/answer/185839) to your Google account (Required)
+- [Create an app password](https://myaccount.google.com/apppasswords).
+
+At the end of creating your app passwords, a password will be displayed; save it, it will be used for the password field when setting up the SMTP server in Immich.
+
+<img src={require('./img/google-app-password.webp').default} title="Authorised redirect URIs" />
+
+## Entering the SMTP credential in Immich
+
+Entering your credential in Immich's email notification settings at `Administration -> Settings -> Notification Settings`
+
+<img src={require('./img/email-settings.png').default} width="80%" title="SMTP settings" />