implemented --help

src/main.c

@@ -10,6 +10,23 @@ void die(char *s) {
     fprintf(stderr, "fatal: %s\n", s);
     exit(1);
 }
+
+void usage(void) {
+    printf(
+            "cards: A terminal flashcard program written in C using ncurses.\n"
+            "Usage:\n"
+            "    cards [filename]\n"
+            "        Read cards from filename. Filename must be a tab separated value file\n"
+            "        containing exactly two fields. The first field should contain the text for\n"
+            "        the \"front\" of the card. The second field should contain the text for the\n"
+            "        back. Each line is read as a separate card. Note that it must be delimited\n"
+            "        by hard tabs (ascii 9), NOT spaces.\n"
+            "    cards --help\n"
+            "        Display this help message.\n"
+          );
+    exit(0);
+}
+
 char *fgetl(FILE *stream) { size_t s_sz = 1; // +1 for null byte
     char *s = NULL;
     char c;
@@ -42,7 +59,9 @@ int main(int argc, char **argv) {
     char k = '\0', *help_message;
 
     if (argc < 2)
-        die("filename required");
+        die("arg required");
+    if (!strcmp(argv[1], "--help"))
+        usage();
 
     cards = card_parse_csv(argv[1], &cards_ct);