Clarify explanation of link_to helper in jsblogger

I've coached a handful of newbies using the Blogger tutorial, and a lot of people have been confused by the link_to explanation. The confusion mainly stems from
```ruby
link_to "Text You Want the Link to Say", where_the_link_should_point
```
because people don't realize that it's pseudo-code and try to put it into their applications.

I'm not sure this change is perfect, but I think it does clarify a confusing spot in the tutorial.

Credit goes to @mepps who's working through the tutorial and suggested that this needed clarification.