fix #522, also clarify text

[ott2]

I clarified that Model 2 is wrong, simplified some of the text, and used code style for the variable names to match other later tutorials.

Edit: lightly copy-edited some other tutorials.

Edit: fixed name of @JoanEspasa to match articles as published (Joan Espasa, not Joan Espasa Arxer). The author name on document itself is currently Espasa Arxer, is this right?

[ozgurakgun]

Thanks Andras!