doc: document that the obj output format GROUP directive is cumulative

The GROUP directive can now be specified more than once for a group,
and the result is cumulative (the union of all specified groups.)

Signed-off-by: KO Myung-Hun <komh78@gmail.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

Author: komh

doc/changes.src

@@ -27,6 +27,10 @@ It is the production version of NASM since 2025.
 \b The unofficial but obvious alternate form \c{TEST reg,mem} was not
    accepted by NASM 3.00; corrected.
 
+\b For the \c{obj} output format, multiple \c{GROUP} directives can
+   now be specified for the same group; the resulting group includes
+   all sections specified in all \c{GROUP} directives for the group.
+
 
 \S{cl-3.00} Version 3.00
 

doc/outfmt.src

@@ -327,6 +327,10 @@ A group does not have to contain any segments; you can still make
 you are referring to. OS/2, for example, defines the special group
 \c{FLAT} with no segments in it.
 
+\c{GROUP} is cumulative. The above example can be done like this:
+
+\c group dgroup data
+\c group dgroup bss
 
 \S{uppercase} \i\c{UPPERCASE}: Disabling Case Sensitivity in Output