Fixed link to information on using placeholders outside of the CMS. (#…

…442)

It was changed incorrectly in 065748e.

README.rst

@@ -258,7 +258,7 @@ within ``Placeholder`` fields.
 If you need to allow additional plugins to be embedded in a HTML field, convert the ``HTMLField`` to a ``Placeholderfield``
 and configure the placeholder to only accept TextPlugin. For more information on using placeholders outside of the CMS see:
 
-http://docs.django-cms.org/en/latest/introduction/templates_placeholders.html
+http://docs.django-cms.org/en/latest/how_to/placeholders.html
 
 
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