desktop: improve help blurb for various cases

- tdf#109202 fix was missing --convert-images-to example
- its not the mimetype, but the filter name that's needed
- also add backslash line continuation where example cmd line
  overflows

Change-Id: I80a461eb4a6ae5c9268bc0f888abd43a179c7a68
Reviewed-on: https://gerrit.libreoffice.org/59722Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

desktop/source/app/cmdlinehelp.cxx

@@ -144,12 +144,12 @@ namespace desktop
         "                       of each immediately. Files are closed after the showing.\n"
         "                       Files other than Impress documents are opened in\n"
         "                       default mode , regardless of previous mode.\n"
-        "   --convert-to OutputFileExtension[:OutputFilterName] \n"
+        "   --convert-to OutputFileExtension[:OutputFilterName] \\\n"
         "     [--outdir output_dir] [--convert-images-to]\n"
         "                       Batch convert files (implies --headless). If --outdir\n"
         "                       isn't specified, then current working directory is used\n"
         "                       as output_dir. If --convert-images-to is given, its\n"
-        "                       parameter is taken as the target MIME format for *all*\n"
+        "                       parameter is taken as the target filter format for *all*\n"
         "                       images written to the output format. If --convert-to is\n"
         "                       used more than once, the last value of OutputFileExtension\n"
         "                       [:OutputFilterName] is effective. If --outdir is used more\n"
@@ -157,7 +157,8 @@ namespace desktop
         "                   --convert-to pdf *.odt\n"
         "                   --convert-to epub *.doc\n"
         "                   --convert-to pdf:writer_pdf_Export --outdir /home/user *.doc\n"
-        "                   --convert-to \"html:XHTML Writer File:UTF8\" *.doc\n"
+        "                   --convert-to \"html:XHTML Writer File:UTF8\" \\\n"
+        "                                --convert-images-to \"jpg\" *.doc\n"
         "                   --convert-to \"txt:Text (encoded):UTF8\" *.doc\n"
         "   --print-to-file [--printer-name printer_name] [--outdir output_dir]\n"
         "                       Batch print files to file. If --outdir is not specified,\n"