Explicitly ignore common text/document file suffixes

Ignore/do not process .txt, .rtf, .md, .nfo, .pdf, and .doc files.

src/ZuluSCSI_disk.cpp

@@ -465,7 +465,7 @@ bool scsiDiskFilenameValid(const char* name)
     if (extension)
     {
         const char *ignore_exts[] = {
-            ".rom_loaded", ".cue",
+            ".rom_loaded", ".cue", ".txt", ".rtf", ".md", ".nfo", ".pdf", ".doc",
             NULL
         };
         const char *archive_exts[] = {