Add docs for cakephp/cakephp#17750

Author: markstory

en/appendices/5-1-migration-guide.rst

@@ -166,3 +166,5 @@ Helpers
   * ``stripProtocol``: Strips ``http://`` and ``https://`` from the beginning of the link. Default off.
   * ``maxLength``: The maximum length of the link label. Default off.
   * ``ellipsis``: The string to append to the end of the link label. Defaults to UTF8 version.
+- ``HtmlHelper::meta()`` can now create a meta tag containing the current CSRF
+  token using ``meta('csrfToken')``.

en/views/helpers/html.rst

@@ -137,14 +137,15 @@ key in the $attributes parameter to ``true``, ie - ``['block' => true]``.
 If you set the "type" attribute using the $attributes parameter,
 CakePHP contains a few shortcuts:
 
-======== ======================
- type     translated value
-======== ======================
-html     text/html
-rss      application/rss+xml
-atom     application/atom+xml
-icon     image/x-icon
-======== ======================
+=========  ======================
+ type       translated value
+=========  ======================
+html       text/html
+rss        application/rss+xml
+atom       application/atom+xml
+icon       image/x-icon
+csrfToken  The current CSRF token
+=========  ======================
 
 .. code-block:: php
 
@@ -215,6 +216,9 @@ In addition to making predefined meta tags, you can create link elements::
 Any attributes provided to meta() when called this way will be added to the
 generated link tag.
 
+.. versionchanged:: 5.1.0
+   The ``csrfToken`` type was added.
+
 Linking to Images
 -----------------