docs: Improve INCLUDES section documentation in jail.conf.5

Add detailed examples and explanations for the [INCLUDES] section:
- Explain that files are relative to the configuration directory
- Document support for multiple files and globbing patterns
- Provide practical examples for common use cases
- Add note about missing file behavior

Closes #4076

man/jail.conf.5

@@ -87,6 +87,28 @@ indicates that the specified file is to be parsed before the current file.
 .TP
 .B after
 indicates that the specified file is to be parsed after the current file.
+.PP
+The [INCLUDES] section allows you to include configuration files relative to the directory of the current configuration file. Multiple files can be specified by separating them with whitespace. Globbing patterns using '*' and '?' are supported.
+.PP
+Examples:
+.RS
+.nf
+# Include a single file before the current configuration
+[INCLUDES]
+before = common.conf
+
+# Include multiple files
+[INCLUDES]
+before = common.conf paths-debian.conf
+after = custom.local
+
+# Include files matching a glob pattern
+[INCLUDES]
+before = /etc/fail2ban/paths-*.conf
+.fi
+.RE
+.PP
+Note: If an included file does not exist, fail2ban will currently ignore it without warning. Ensure that file paths are correct to avoid misconfigurations.
 .RE
 
 Using Python "string interpolation" mechanisms, other definitions are allowed and can later be used within other definitions as %(name)s.