dunst.1: Document drop-in support.

Also some refinements to the FILES section.

docs/dunst.1.pod

@@ -107,38 +107,57 @@ missed notifications after returning to the computer.
 =head1 FILES
 
 These are the base directories dunst searches for configuration files in
-descending order of imortance:
+I<descending order of imortance>:
 
-=over 4
+=over 8
+
+=item C<$XDG_CONFIG_HOME>
+
+This is the most important directory. (C<$HOME/.config> if unset or empty)
 
-$XDG_CONFIG_HOME ($HOME/.config if unset or empty)
+=item C<$XDG_CONFIG_DIRS>
 
-$XDG_CONFIG_DIRS (:-separated list of base directories in descending order
-of importance; ##SYSCONFDIR## if unset or empty)
+This, like C<$PATH> for instance, is a :-separated list of base directories
+in I<descending order of importance>.
+(F<##SYSCONFDIR##> if unset or empty)
 
 =back
 
-Dunst will search these directories for the following relative path:
+Dunst will search these directories for the following relative file paths:
 
-=over 4
+=over 8
 
-dunst/dunstrc
+=item F<dunst/dunstrc>
 
-=back
+This is the base config and as such the least important in a particular base
+directory.
 
-All settings from all files get applied. Settings in more important files
-override those in less important ones. Settings not present in more imortant
-files are taken from a less important one or from the internal defaults if they
-are not found in any file.
+=item F<dunst/dunstrc.d/*.conf>
 
-=over 4
+These are "drop-ins" (mind the ".d" suffix of the directory).
+They are more important than the base dunstrc in the parent directory, as they
+are considered to be small snippets to override settings.
+The last in lexical order is the most important one, so you can easily change
+the order by renaming them.
+A common approach to naming drop-ins is to prefix them with numbers, i.e.:
 
-=item This is where the default (least important) config file is located:
+    00-least-important.conf
+    01-foo.conf
+    20-bar.conf
+    99-most-important.conf
 
-##SYSCONFDIR##/dunst/dunstrc
+The only requirements are that the name of the file must have the correct
+suffix and the first non-blank line that is not a comment must be a section or
+rule identifier.
 
 =back
 
+All settings from all files get applied. Settings in more important files
+override those in less important ones.
+Settings not present in more imortant files get their value from a less
+important one or from the internal defaults if respective key is not found in
+any file.
+
 =head1 AUTHORS
 
 Written by Sascha Kruse <[email protected]>