doc: Document extra Emacs-Debbugs configurations.

* doc/contributing.texi (Viewing Bugs within Emacs): Document
debbugs-gnu-default-packages, debbugs-gnu-default-severities.
(Debbugs User Interfaces): Likewise, and mention debbugs-gnu-guix-search.

Suggested-by: Michael Albinus <michael.albinus@gmx.de>
Change-Id: I8e9026bc394b0cf674c8498ca713c332e48c2700

doc/contributing.texi

@@ -386,6 +386,7 @@ copyright-update}.  If you want to do it automatically after each buffer
 save then add @code{(add-hook 'after-save-hook 'copyright-update)} in
 Emacs.
 
+@node Viewing Bugs within Emacs
 @subsection Viewing Bugs within Emacs
 
 Emacs has a nice minor mode called @code{bug-reference}, which, when
@@ -453,6 +454,13 @@ configuration file:
           (group (zero-or-one "cgi/bugreport.cgi?bug="))
           (group-n 3 (one-or-more digit))
           line-end))
+
+;; Reduce the number of prompts with 'M-x debbugs-gnu'.
+(setq debbugs-gnu-default-packages '("guix" "guix-patches"))
+
+;; Show feature requests.
+(setq debbugs-gnu-default-severities
+ '("serious" "important" "normal" "minor" "wishlist"))
 @end lisp
 
 For more information, refer to @ref{Bug Reference,,, emacs, The GNU
@@ -1975,6 +1983,15 @@ For example, to list all open issues on @code{guix-patches}, hit:
 @kbd{C-u} @kbd{M-x} debbugs-gnu @kbd{RET} @kbd{RET} guix-patches @kbd{RET} n y
 @end example
 
+For a more convenient (shorter) way to access both the bugs and patches
+submissions, you may want to configure the
+@code{debbugs-gnu-default-packages} and
+@code{debbugs-gnu-default-severities} Emacs variables (@pxref{Viewing
+Bugs within Emacs}).
+
+To search for bugs, @samp{@kbd{M-x} debbugs-gnu-guix-search} can be
+used.
+
 @xref{Top,,, debbugs-ug, Debbugs User Guide}, for more information on
 this nifty tool!