documentation: update kernel-doc-nano-HOWTO information

Remove comments about function short descriptions not allowed to be on
multiple lines (that was fixed/changed recently).

Add comments that function "section header:" names need to be unique per
function/struct/union/typedef/enum.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/kernel-doc-nano-HOWTO.txt

@@ -214,11 +214,13 @@ The format of the block comment is like this:
  * (section header: (section description)? )*
 (*)?*/
 
-The short function description ***cannot be multiline***, but the other
-descriptions can be (and they can contain blank lines).  If you continue
-that initial short description onto a second line, that second line will
-appear further down at the beginning of the description section, which is
-almost certainly not what you had in mind.
+All "description" text can span multiple lines, although the
+function_name & its short description are traditionally on a single line.
+Description text may also contain blank lines (i.e., lines that contain
+only a "*").
+
+"section header:" names must be unique per function (or struct,
+union, typedef, enum).
 
 Avoid putting a spurious blank line after the function name, or else the
 description will be repeated!