feature #4883 Global dump (nicolas-grekas)

This PR was merged into the 2.6 branch.

Discussion
----------

Global dump

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | -

Commits
-------

4121dbd [VarDumper] add a tip about global dump() availability

components/var_dumper/introduction.rst

@@ -62,6 +62,17 @@ current PHP SAPI:
     You'll also learn how to change the format or redirect the output to
     wherever you want.
 
+.. tip::
+
+    In order to have the ``dump()`` function always available when running
+    any PHP code, you can install it globally on your computer:
+
+    #. Run ``composer global require symfony/var-dumper``;
+    #. Add ``auto_prepend_file = ${HOME}/.composer/vendor/autoload.php``
+       to your ``php.ini`` file;
+    #. From time to time, run ``composer global update`` to have the latest
+       bug fixes.
+
 DebugBundle and Twig Integration
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