[FEATURE] Document Navigation title

Documentation/WritingReST/Reference/Menus/NavigationTitle.rst

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+:navigation-title: Navigation title
+
+..  _navigation-title:
+
+=================================================
+Navigation title: A page title displayed in menus
+=================================================
+
+It is possible to define a different, usually shorter, title for a page to be
+displayed in menus.
+
+While the title of a page is a very important tool to pass information to
+both the readers and search engines including our internal elastic search,
+elaborate titles usually take up to much space within the menu, the breadcrumb
+etc.
+
+For example, the title of the page you are currently reading is quite long:
+`Navigation title: A page title displayed in menus`. This title is also used
+as automatic title in references, unless otherwise specified:
+:ref:`navigation-title`.
+
+However in the main menu and in the breadcrumb the shorter navigation title
+is displayed.
+
+A navigation title can be defined as follows:
+
+..  code-block:: rst
+    :capition: SomePage.rst
+
+    :navigation-title: Navigation title
+
+    ..  include:: /Includes.rst.txt
+    ..  _navigation-title:
+
+    =================================================
+    Navigation title: A page title displayed in menus
+    =================================================
+
+    [...]
+
+    For example, the title of the page you are currently reading is quite long:
+    `Navigation title: A page title displayed in menus`. This title is also used
+    as automatic title in references, unless otherwise specified:
+    :ref:`navigation-title`.