[PULL 2/3] docs/devel/qapi-code-gen: Belatedly document feature documentation

[Markus Armbruster <armbru@redhat.com>]

Commit 6a8c0b5102 "qapi: Add feature flags to struct types" neglected
to document how to document feature flags.  Make up for that.

Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20211026111023.76937-3-armbru@redhat.com>
[Editing accident fixed]
---
 docs/devel/qapi-code-gen.rst | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst
index b5761f60cd..a3b5473089 100644
--- a/docs/devel/qapi-code-gen.rst
+++ b/docs/devel/qapi-code-gen.rst
@@ -956,15 +956,16 @@ definition must have documentation.
 Definition documentation starts with a line naming the definition,
 followed by an optional overview, a description of each argument (for
 commands and events), member (for structs and unions), branch (for
-alternates), or value (for enums), and finally optional tagged
-sections.
+alternates), or value (for enums), a description of each feature (if
+any), and finally optional tagged sections.
 
-Descriptions of arguments can span multiple lines.  The description
-text can start on the line following the '\@argname:', in which case it
-must not be indented at all.  It can also start on the same line as
-the '\@argname:'.  In this case if it spans multiple lines then second
-and subsequent lines must be indented to line up with the first
-character of the first line of the description::
+The description of an argument or feature 'name' starts with
+'\@name:'.  The description text can start on the line following the
+'\@name:', in which case it must not be indented at all.  It can also
+start on the same line as the '\@name:'.  In this case if it spans
+multiple lines then second and subsequent lines must be indented to
+line up with the first character of the first line of the
+description::
 
  # @argone:
  # This is a two line description
@@ -986,6 +987,12 @@ The number of spaces between the ':' and the text is not significant.
 Extensions added after the definition was first released carry a
 '(since x.y.z)' comment.
 
+The feature descriptions must be preceded by a line "Features:", like
+this::
+
+  # Features:
+  # @feature: Description text
+
 A tagged section starts with one of the following words:
 "Note:"/"Notes:", "Since:", "Example"/"Examples", "Returns:", "TODO:".
 The section ends with the start of a new section.
-- 
2.31.1