These descriptions would go in the autoindex configuration file. It is commonly in a subdirectory where you find find httpd.conf. Usually in extras or conf.d or something to that effect. Enough talk, here is the list!
AddDescription "3GP Video" .3gp AddDescription "3GP2 Video" .3g2 AddDescription "7-Zip Archive" .7z AddDescription "Adobe Flash Application" .swf AddDescription "Adobe Flex Project" .fxp AddDescription "Adobe Portable Document Format" .pdf AddDescription "Assembler Source File" .s AddDescription "Audio Interchange File" .aif AddDescription "Audio Video Interleave Video" .avi AddDescription "Binary CPIO Archive" .bcpio AddDescription "Binary Data" .bin AddDescription "Bitmap Image File" .bmp AddDescription "BitTorrent File" .torrent #AddDescription "Blackberry COD File" .cod AddDescription "Bourne Shell Script" .sh AddDescription "Bzip Archive" .bz AddDescription "Bzip2 Archive" .bz2 AddDescription "C Shell Script" .csh AddDescription "C Source File" .c AddDescription "Cascading Style Sheet" .css AddDescription "CPIO Archive" .cpio AddDescription "Debian Package" .deb AddDescription "Document Type Definition" .dtd AddDescription "Electronic Publication" .epub AddDescription "E-Mail Message" .eml AddDescription "Flash Video" .f4v .flv #AddDescription "Fortran Source File" .f .f77 .f90 #AddDescription "GhostScript Font" .gsf #AddDescription "GNU Tar File" .gtar #AddDescription "GNU Texinfo Document" .texinfo AddDescription "GIF Image" .gif #AddDescription "H.261 Video" .h261 #AddDescription "H.263 Video" .h263 AddDescription "H.264 Video" .h264 AddDescription "HTML Document" .html .htm #AddDescription "HyperText Application Language" .hal AddDescription "Icon Image" .ico AddDescription "Image Exchange Format" .ief AddDescription "Java Archive" .jar AddDescription "Java Class" .class AddDescription "Java Source File" .java AddDescription "Java Serialized Object" .ser AddDescription "JavaScript File" .js AddDescription "JSON File" .json AddDescription "JPEG Image" .jpg .jpeg #AddDescription "JPGVideo" .jpgv #AddDescription "LaTeX File" .latex AddDescription "M3U Playlist" .m3u AddDescription "M4V Video" .m4v #AddDescription "Microsoft Access Database" AddDescription "MS Executable File" .exe #AddDescription "MS Cabinet File" .cab AddDescription "MS Excel File" .xls .xlsx #AddDescription "MS HTML Help File" .chm #AddDescription "MS Information Card" .crd #AddDescription "Microsoft Money" .mny #AddDescription "MS Powerpoint Presentation" .ppt AddDescription "MS Windows Media Audio" .wma AddDescription "MS Word Document" .doc .docx #AddDescription "MPEG Audio" .mpga AddDescription "MPEG Video" .mpeg .mpg AddDescription "MP3 Audio" .mp3 AddDescription "MPEG-4 Audio File" .mp4a AddDescription "MPEG-4 Video File" .mp4 #AddDescription "MPEG4 Application" .mp4 AddDescription "Ogg Audio" .oga AddDescription "Ogg Video" .ogv #AddDescription "MS Windows DLL File" .dll AddDescription "Open Web Media Audio File" .weba AddDescription "Open Web Media Video File" .webm AddDescription "OpenType Font" .otf AddDescription "TrueType Font" .ttf AddDescription "Pascal Source File" .p AddDescription "Adobe Photoshop Document" .psd AddDescription "PNG Image" .png AddDescription "PostScript File" .ai #AddDescription "Adobe Illustrator File" .ai AddDescription "PGP Signature" .pgp AddDescription "Quicktime Video" .qt AddDescription "RAR Archive" .rar AddDescription "Rich Text File" .rtf .rtx AddDescription "SVG Image" .svg AddDescription "PHP Archive" .phar AddDescription "TIFF Image" .tiff AddDescription "Tar Archive" .tar AddDescription "TeX File" .tex AddDescription "Plain Text File" .txt #AddDescription "URI List" .uri AddDescription "vCard" .vcf AddDescription "UUEncoded File" .uu AddDescription "Windows Help File" .hlp AddDescription "X.509 Certificate" .der .crt .x509 AddDescription "XML File" .xml .atom .rss AddDescription "XSLT File" .xslt AddDescription "YAML File" .yml AddDescription "Python Script" .py AddDescription "Perl Script" .pl .perl .cgi AddDescription "PHP Script" .php .php1 .php2 .php3 .php4 .phtml AddDescription "PHP Source File" .phps AddDescription "PHP Test File" .phpt AddDescription "SQL Dump File" .sql AddDescription "Zip Archive" .z .Z .zip AddDescription "C Header File" .h AddDescription "C++ Source File" .cpp .c++ .cxx AddDescription "Patch File" .patch AddDescription "Diff File" .diff AddDescription "Gzip Compressed File" .gz AddDescription "XZ Compressed File" .xz AddDescription "Server Parsed HTML File" .shtml AddDescription "File Manifest" .manifest
