Adding guidance for referencing man pages

Author: bergerhoffer

supplementary_style_guide/style_guidelines/formatting.adoc

@@ -8,6 +8,23 @@ Follow the _IBM Style_ guide advice of _day Month year_ for date formats, for ex
 
 When the format _day Month year_ causes a presentation or clarity issue, use _Month day, year_ (for example, October 3, 2019) instead.
 
+[[man-pages]]
+== Man page references
+
+When referencing a man page in an "Additional resources" section, use the following format:
+
+* `_<man_page_name>_(_<section_number>_)` man page on your system
+
+Do not link to a website that contains the man page information. The contents of a man page might vary between systems or package versions, so users must run the `man` command on the target system to view the system-specific information for the named command or utility.
+
+.Example: Single man page
+
+* `sudoers(5)` man page on your system
+
+.Example: Multiple man pages
+
+* `nmcli(1)`, `nm-settings(5)`, and `sudoers(5)` man pages on your system
+
 [[non-breaking-spaces]]
 == Non-breaking spaces