Add Gitea Fastmail SMTP configuration information

src/hosting/gitea.md

@@ -289,6 +289,26 @@ On your local machine:
 scp <user>@<remote_ip>:/home/git/<backup-file> d:\
 ```
 
+### SMTP setup with Fastmail
+1. `sudo vim /etc/gitea/app.ini`
+2. Update `[mailer]` per the below.
+3. `sudo systemctl restart gitea`
+4. Send a test email from Gitea's `/admin/config`.
+
+```
+[mailer]
+ENABLED        = true
+FROM           = gitea@mydomain.com
+MAILER_TYPE    = smtp
+SMTP_ADDR      = smtp.fastmail.com
+SMTP_PORT      = 465
+IS_TLS_ENABLED = true
+USER           = `your.email@fastmail.com`
+PASSWD         = `password`
+```
+
+`USER` must be your primary Fastmail email. `PASSWD` is an application password. `FROM` can be your primary or an alias email.
+
 ### Useful commands
 ```bash
 # View Gitea disk usage.