perlPackages: add meta.mainProgram to pacakges with single executable

where the executable's name differs from the packages `name` or `pname`

pkgs/development/perl-modules/WWW-YoutubeViewer/default.nix

@@ -25,7 +25,8 @@ buildPerlPackage rec {
   meta = with lib; {
     description = "A lightweight application for searching and streaming videos from YouTube";
     homepage = "https://github.com/trizen/youtube-viewer";
-    maintainers = with maintainers; [ woffs ];
     license = with licenses; [ artistic2 ];
+    maintainers = with maintainers; [ woffs ];
+    mainProgram = "youtube-viewer";
   };
 }

pkgs/development/perl-modules/ham/default.nix

@@ -37,6 +37,7 @@ buildPerlPackage {
     homepage = "https://github.com/kernkonzept/ham";
     license = "unknown"; # should be gpl2, but not quite sure
     maintainers = with lib.maintainers; [ aw ];
+    mainProgram = "ham";
     platforms = lib.platforms.unix;
   };
 }