Update README.md

Just a small change of wording. Need to create release 1.0.1 to for file exchange.

Author: slreq

README.md

@@ -141,7 +141,7 @@ Keep in mind that a smaller stopThreshold can give beeter accuracy, but it will
 reach the answer.
 
 #### outfile
-This optional parameter is used to output an animation gif
+This optional parameter is used to output an animation gif file. It can be set like this:
 
 ```
 agd.outfile='animateGraDes.gif';