minor #15817 Update pull_requests.rst (gnito-org)

This PR was submitted for the 5.4 branch but it was merged into the 4.4 branch instead.

Discussion
----------

Update pull_requests.rst

Adding a link to the SymfonyCasts video tutorial on contributing code.

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/releases for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `5.x` for features of unreleased versions).

-->

Commits
-------

da0bdb4 Update pull_requests.rst

Author: javiereguiluz

contributing/code/pull_requests.rst

@@ -4,6 +4,9 @@ Proposing a Change
 A pull request, "PR" for short, is the best way to provide a bug fix or to
 propose enhancements to Symfony.
 
+If you prefer video tutorials instead of a wall of text, then please watch
+this comprehensive and free `Contributing Back To Symfony`_ tutorial by `SymfonyCasts.com`_. 
+
 Step 1: Check existing Issues and Pull Requests
 -----------------------------------------------
 
@@ -529,3 +532,5 @@ before merging.
 .. _`Symfony Slack`: https://symfony.com/slack-invite
 .. _`Travis-CI`: https://travis-ci.org/symfony/symfony
 .. _`Psalm phar is installed`: https://psalm.dev/docs/running_psalm/installation/
+.. _`Contributing Back To Symfony`: https://symfonycasts.com/screencast/contributing
+.. _`SymfonyCasts.com`: https://symfonycasts.com