Update wording of ?news about heading levels(PR#18891, by Michael Chirico).

git-svn-id: https://svn.r-project.org/R/trunk@88203 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: hornik

src/library/utils/man/news.Rd

@@ -93,12 +93,14 @@ news(query, package = "R", lib.loc = NULL, format = NULL,
 
 \subsection{\file{NEWS.md}}{
   File \file{NEWS.md} should contain the news in Markdown (following the
-  \I{CommonMark} (\url{https://commonmark.org/}) specification), with the
-  primary heading level giving the version number after a prefix
-  followed by a space, and optionally followed by a space and a
-  parenthesized ISO 8601 format date.  Where available, secondary
-  headings are taken to indicate categories.  To accommodate for common
-  practice, news entries are only split down to the category level.
+  \I{CommonMark} (\url{https://commonmark.org/}) specification), with a
+  primary heading level (e.g., ATX heading \code{#} or \code{##}) giving
+  the version number after a prefix followed by a space, and optionally
+  followed by a space and a parenthesized ISO 8601 format date.  Where
+  available, secondary headings (i.e., one heading level higher than
+  the primary heading level) are taken to indicate categories.  To
+  accommodate for common practice, news entries are only split down to
+  the category level.
 }
 
 \subsection{\file{NEWS}}{