Fix formatting for Mailer.FROM address example in configuration cheat sheet (#296)

This example is incorrect.

wrong:

<img width="1058" alt="wrong-1.png" src="attachments/1cb3b95b-c3e4-4213-aeff-13e518021536">

<img width="442" alt="wrong-2.png" src="attachments/212aa79f-bbb7-457a-a0b8-fc7572f6d497">

<img width="1201" alt="wrong-3.png" src="attachments/32fde98a-d987-475c-9f88-d563c177ad24">

correct:

<img width="1034" alt="correct-1.png" src="attachments/b4993846-eec2-4e7c-8adc-11fc335216dc">

<img width="410" alt="correct-2.png" src="attachments/419ad32c-4080-462e-af5e-8fc9f63727a7">

Reviewed-on: https://gitea.com/gitea/docs/pulls/296
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: dangjinghao <dangjinghaoemail@163.com>
Co-committed-by: dangjinghao <dangjinghaoemail@163.com>

docs/administration/config-cheat-sheet.md

@@ -819,7 +819,7 @@ and
   - Please note: authentication is only supported when the SMTP server communication is encrypted with TLS (this can be via `STARTTLS`) or SMTP host is localhost. See [Email Setup](email-setup.md) for more information.
 - `ENABLE_HELO`: **true**: Enable HELO operation.
 - `HELO_HOSTNAME`: **(retrieved from system)**: HELO hostname.
-- `FROM`: **_empty_**: Mail from address, RFC 5322. This can be just an email address, or the "Name" `\<email@example.com\>` format.
+- `FROM`: **_empty_**: Mail from address, RFC 5322. This can be just an email address, or the `"Name" <email@example.com>` format.
 - `ENVELOPE_FROM`: **_empty_**: Address set as the From address on the SMTP mail envelope. Set to `<>` to send an empty address.
 - `FROM_DISPLAY_NAME_FORMAT`: **`{{ .DisplayName }}`**: If gitea sends mails on behave of users, it will just use the name also displayed in the WebUI. If you want e.g. `Mister X (by CodeIt) <gitea@codeit.net>`, set it to `{{ .DisplayName }} (by {{ .AppName }})`. Available Variables: `.DisplayName`, `.AppName` and `.Domain`.
 - `SUBJECT_PREFIX`: **_empty_**: Prefix to be placed before e-mail subject lines.