Update forms.rst

Two small corrections to what is currently section 6.3.5:
1) The about page is missing from urls.py and it was added previously in the tutorial, which can be a bit confusing for a user.  Looks like it pops up again in a later chapter, so it's probably worth keeping here.
2) The url pattern for the category appears to be wrong.  I wasn't sure if at first this was an intentional pattern change in the tutorial, given the description that follows this block of code.  However, later in the tutorial it reverts back to this pattern so I think this might be a little bust.  That said, if this change is accepted, I think the descriptions shortly following this code block may need to be updated.