added doxygen documentation

misc/factorial_large_number.c

@@ -1,3 +1,8 @@
+/**
+ * @file
+ * Compute factorial of arbitrarily large numbers by
+ * storing individual digits in a byte.
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -79,6 +84,9 @@ void multiply(large_num *num, unsigned long n)
     }
 }
 
+/**
+ * main function
+ */
 int main(int argc, char *argv[])
 {
     int number, i;