Fix alignment setting documentation

`alignment` specifies the alignment of the text within the notifications,
not the alignment of the notifications themselves.

docs/dunst.pod

@@ -111,7 +111,7 @@ Shortcut for context menu.
 
 =item B<-alignment position>
 
-Defines the align position of notifications to left/center/right.
+Defines how text should be aligned, can be set to left/center/right.
 
 =item B<-icon_position position>
 

src/settings.c

@@ -214,7 +214,7 @@ void load_settings(char *cmdline_config_path)
                 char *c = option_get_string(
                         "global",
                         "alignment", "-align/-alignment", "",
-                        "Align notifications left/center/right"
+                        "Text alignment left/center/right"
                 );
 
                 if (strlen(c) > 0) {