Added quoting for passwords in sample.app.ini and documentation (#3395)

custom/conf/app.ini.sample

@@ -198,6 +198,7 @@ DB_TYPE = mysql
 HOST = 127.0.0.1:3306
 NAME = gitea
 USER = root
+; Use PASSWD = `your password` for quoting if you use special characters in the password.
 PASSWD =
 ; For "postgres" only, either "disable", "require" or "verify-full"
 SSL_MODE = disable
@@ -342,6 +343,7 @@ KEY_FILE = custom/mailer/key.pem
 FROM =
 ; Mailer user name and password
 USER =
+; Use PASSWD = `your password` for quoting if you use special characters in the password.
 PASSWD =
 ; Send mails as plain text
 SEND_AS_PLAIN_TEXT = false
@@ -464,6 +466,7 @@ SUBJECT = Diagnostic message from server
 HOST =
 ; Mailer user name and password
 USER =
+; Use PASSWD = `your password` for quoting if you use special characters in the password.
 PASSWD =
 ; Receivers, can be one or more, e.g. 1@example.com,2@example.com
 RECEIVERS =

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -118,7 +118,7 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.
 - `HOST`: **127.0.0.1:3306**: Database host address and port.
 - `NAME`: **gitea**: Database name.
 - `USER`: **root**: Database username.
-- `PASSWD`: **\<empty\>**: Database user password.
+- `PASSWD`: **\<empty\>**: Database user password. Use \`your password\` for quoting if you use special characters in the password. 
 - `SSL_MODE`: **disable**: For PostgreSQL only.
 - `PATH`: **data/gitea.db**: For SQLite3 only, the database file path.
 
@@ -185,7 +185,7 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.
 - `FROM`: **\<empty\>**: Mail from address, RFC 5322. This can be just an email address, or
    the "Name" \<email@example.com\> format.
 - `USER`: **\<empty\>**: Username of mailing user (usually the sender's e-mail address).
-- `PASSWD`: **\<empty\>**: Password of mailing user.
+- `PASSWD`: **\<empty\>**: Password of mailing user.  Use \`your password\` for quoting if you use special characters in the password.
 - `SKIP_VERIFY`: **\<empty\>**: Do not verify the self-signed certificates.
    - **Note:** Gitea only supports SMTP with STARTTLS.
 - `USE_SENDMAIL`: **false** Use the operating system's `sendmail` command instead of SMTP.