[Doc] Reword whitespace control note about first-newline removal

The previous wording ("inherited from PHP") was misleading: Twig does
not inherit anything from PHP, it deliberately implements the same
behavior, like Jinja does. The behavior was already explained earlier
in the same section, so just point back to it instead.

doc/templates.rst

@@ -1221,7 +1221,7 @@ Twig supports two modifiers:
 
 * *Line whitespace trimming* via the ``~`` modifier: Removes all whitespace
   (excluding newlines). Using this modifier on the right disables the default
-  removal of the first newline inherited from PHP.
+  removal of the first newline mentioned above.
 
 The modifiers can be used on either side of the tags like in ``{%-`` or ``-%}``
 and they consume all whitespace for that side of the tag. It is possible to use