Fix usage message on gendsa:

1. The dsaparam argument is mandatory and not optional
2. Add a little text what this actually is: a filename

apps/gendsa.c

@@ -137,7 +137,7 @@ char **argv;
 	if (dsaparams == NULL)
 		{
 bad:
-		BIO_printf(bio_err,"usage: gendsa [args] [dsaparams]\n");
+		BIO_printf(bio_err,"usage: gendsa [args] dsaparam-file\n");
 		BIO_printf(bio_err," -out file - output the key to 'file'\n");
 #ifndef NO_DES
 		BIO_printf(bio_err," -des      - encrypt the generated key with DES in cbc mode\n");
@@ -149,6 +149,8 @@ bad:
 		BIO_printf(bio_err," -rand file:file:...\n");
 		BIO_printf(bio_err,"           - load the file (or the files in the directory) into\n");
 		BIO_printf(bio_err,"             the random number generator\n");
+		BIO_printf(bio_err," dsaparam-file\n");
+		BIO_printf(bio_err,"           - a DSA parameter file as generated by the dsaparam command\n");
 		goto end;
 		}