MANUAL: Document use of citations in note styles.

See #6828.

MANUAL.txt

@@ -5359,6 +5359,34 @@ example:
       }
     }
 
+
+## Citations in note styles
+
+Pandoc's citation processing is designed to allow you to
+move between author-date, numerical, and note styles without
+modifying the markdown source.  When you're using a note
+style, avoid inserting footnotes manually. Instead, insert
+citations just as you would in an author-date style---for
+example,
+
+    Blah blah [@foo, p. 33].
+
+The footnote will be created automatically. Pandoc will take
+care of removing the space and moving the note before or
+after the period, depending on the setting of
+`notes-after-punctuation`, as described below in [Other relevant
+metadata fields].
+
+In some cases you may need to put a citation inside a regular
+footnote.  Normal citations in footnotes (such as `[@foo, p.
+33]`) will be rendered in parentheses.  In-text citations (such
+as `@foo [p. 33]`) will be rendered without parentheses. (A
+comma will be added if appropriate.)  Thus:
+
+    [^1]:  Some studies [@foo; @bar, p. 33] show that
+    frubulicious zoosnaps are quantical.  For a survey
+    of the literature, see @baz [chap. 1].
+
 ## Raw content in a style
 
 To include raw content in a prefix, suffix, delimiter, or term,