Update Wolf tutorial with the OBITools3

Wolf-tutorial-with-the-OBITools3.md

@@ -16,6 +16,8 @@ And unzip it:
 		obi import --quality-solexa wolf_tutorial/wolf_F.fastq wolf/reads1
 
 	`--quality-solexa` is the appropriate fastq quality option because it's an old dataset, `wolf_tutorial/wolf_F.fastq` is the path to the file to import, `wolf` is the path to the DMS that will be automatically created, and `reads1` is the name of the view into which the file will be imported.
+        
+	**Note:** If some sequences fail to import, you might need to use the `--input-na-string` option to define the NA string.
 
 2. Import the second set of reads: