First attempt at updating a help file (please let me know if I got it right)

Hi,

I'm trying to learn how to use github to propose edits and updates to the SC Docs.
I did a very minor update to the GrainSin help file as a test (simply changed .send(s) to .add in example SynthDef), verified that it still runs, then I'm making this pull request. It's my first attempt at updating a Help File and I am sort of new to github, so please let me know if I am doing anything wrong or what best practices are. I hope to contribute more often with the Docs from now on. Thanks a lot!

Signed-off-by: Bruno Ruviaro <ruviaro@brubuntu.(none)>