feature symfony#14115 Update pull_requests.rst (noniagriconomie)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead.

Discussion
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Update pull_requests.rst

Fix symfony#14113

Commits
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1988c14 Doc link script rollback option

Author: OskarStark

contributing/code/pull_requests.rst

@@ -196,6 +196,8 @@ want to debug are installed by running ``composer install`` inside it.
     If symlinks to your local Symfony fork cannot be resolved inside your project due to 
     your dev environment (for instance when using Vagrant where only the current project 
     directory is mounted), you can alternatively use the ``--copy`` option.
+    When finishing testing your Symfony code into your project, you can use
+    the ``--rollback`` option to make your project back to its original dependencies.
 
 .. _work-on-your-patch: