dpkg: Document optional -C argument in --help output

Closes: #763000

debian/changelog

@@ -117,6 +117,7 @@ dpkg (1.17.14) UNRELEASED; urgency=low
   * Double the dpkg files database hash table size to the closest 2^18 prime.
     Times have changed, and it's common to have at least these many files.
     This reduces the amount of collisions.
+  * Document optional dpkg -C argument in --help output. Closes: #763000
 
   [ Raphaël Hertzog ]
   * Explain better in deb-triggers(5) why interest/activate-noawait should be

src/main.c

@@ -104,7 +104,7 @@ usage(const struct cmdinfo *ci, const char *value)
 "  -L|--listfiles <package> ...     List files `owned' by package(s).\n"
 "  -l|--list [<pattern> ...]        List packages concisely.\n"
 "  -S|--search <pattern> ...        Find package(s) owning file(s).\n"
-"  -C|--audit                       Check for broken package(s).\n"
+"  -C|--audit [<package> ...]       Check for broken package(s).\n"
 "  --add-architecture <arch>        Add <arch> to the list of architectures.\n"
 "  --remove-architecture <arch>     Remove <arch> from the list of architectures.\n"
 "  --print-architecture             Print dpkg architecture.\n"