docs: add email & Discord notification info (#1251)

* docs: add email & Discord notification info

* docs: update TOC

docs/using-overseerr/notifications/email.md

@@ -0,0 +1,54 @@
+# Email
+
+{% hint style="info" %}
+The following email notification types are sent to _all_ users with the **Manage Requests** permission, as these notification types are intended for application administrators rather than end users:
+
+- Media Requested
+- Media Automatically Approved
+- Media Failed
+
+On the other hand, the email notification types below are only sent to the user who submitted the request:
+
+- Media Approved
+- Media Declined
+- Media Available
+
+{% endhint %}
+
+## Configuration
+
+### Sender Address (required)
+
+Set this to the email address you would like to appear in the "from" field of the email message.
+
+Depending on your email provider, this may need to be an address you own. For example, Gmail requires this to be your actual email address.
+
+### Sender Name (optional)
+
+Configure a friendly name for the email sender.
+
+### SMTP Host
+
+Set this to the hostname or IP address of your SMTP host/server.
+
+### SMTP Port
+
+Set this to a supported port number for your SMTP host. `465` and `587` are commonly used.
+
+### Enable SSL (optional)
+
+This setting should only be enabled for ports that use [implicit SSL/TLS](https://tools.ietf.org/html/rfc8314) (e.g., port `465` in most cases).
+
+For servers that support [opportunistic TLS/STARTTLS](https://en.wikipedia.org/wiki/Opportunistic_TLS) (typically via port `587`), this setting should **not** be enabled.
+
+### SMTP Username & Password
+
+{% hint style="info" %}
+If your account has two-factor authentication enabled, you may need to create an application password instead of using your account password.
+{% endhint %}
+
+Configure these values as appropriate to authenticate with your SMTP host.
+
+### PGP Private Key & Password (optional)
+
+Configure these values to enable encrypting and signing of email messages using [OpenPGP](https://www.openpgp.org/). Note that individual users must also have their PGP public keys enabled in their user settings in order for PGP encryption to be used.