Mention Rector in the upgrading articles

Author: javiereguiluz

setup/upgrade_major.rst

@@ -54,6 +54,12 @@ And sometimes, the warning may come from a third-party library or bundle
 that you're using. If that's true, there's a good chance that those deprecations
 have already been updated. In that case, upgrade the library to fix them.
 
+.. tip::
+
+    `Rector`_ is a third-party project that automates the upgrading and
+    refactoring of PHP projects. Rector includes some rules to fix certain
+    Symfony deprecations automatically.
+
 Once all the deprecation warnings are gone, you can upgrade with a lot
 more confidence.
 
@@ -314,3 +320,4 @@ Classes in the ``vendor/`` directory are always ignored.
        Now, you can safely allow ``^6.0`` for the Symfony dependencies.
 
 .. _`PHP CS Fixer`: https://github.com/friendsofphp/php-cs-fixer
+.. _`Rector`: https://github.com/rectorphp/rector

setup/upgrade_minor.rst

@@ -84,6 +84,12 @@ included in the Symfony directory that describes these changes. If you follow
 the instructions in the document and update your code accordingly, it should be
 safe to update in the future.
 
+.. tip::
+
+    `Rector`_ is a third-party project that automates the upgrading and
+    refactoring of PHP projects. Rector includes some rules to fix certain
+    Symfony deprecations automatically.
+
 These documents can also be found in the `Symfony Repository`_.
 
 .. _updating-flex-recipes:
@@ -92,3 +98,4 @@ These documents can also be found in the `Symfony Repository`_.
 
 .. _`Symfony Repository`: https://github.com/symfony/symfony
 .. _`UPGRADE-5.4.md`: https://github.com/symfony/symfony/blob/5.4/UPGRADE-5.4.md
+.. _`Rector`: https://github.com/rectorphp/rector