[css3-selectors][css-selectors] Comments on Section 4

1)  The sentence "One pseudo-element may be appended to the last sequence of
     simple selectors." in paragraph 3 may be clearer as:

   One pseudo-element may be appended to the last sequence of simple selectors in
   a selector.

2)  The link to "content selector" in paragraph 3 points to the infamous section
     6.6.6 (the one that has been removed).  This link should probably be removed
     too.

-Boris