update readme file

README.md

@@ -29,6 +29,20 @@ inputs:
 Outputs:
 none
 
+You can also use a credential file as shown in /test:
+```
+credentials = jsondecode(fileread('credentials.json'));
+opts = struct("username", credentials.username, "password",  credentials.password ,"maxDuration", false);
+```
+where the json file is so created:
+```
+{
+    "username":"ygagarin",
+    "password":":YG_password"
+}
+```
+
+
 When the user will succesfully login via the login class method `MatMust_login()` a auth.json file with the authorization tocken will be wrote on your workingdirectory root.  
 
 ### MatMust_logincheck

matlab/test/credentials.json

-{
-	"username":"ygagarin",
-	"password":":YG_password"
-}
\ No newline at end of file