bug #6704 Encountered an error when following the steps for contribution (chancegarcia)

This PR was merged into the 2.7 branch.

Discussion
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Encountered an error when following the steps for contribution

Encountered an error when following the steps for contribution. Updated the contribution overview to reflect how to avoid that error when transitioning between steps 3 and 4 in `Your First Documentation Contribution`.

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e2fabe5 Encountered an error when following the steps for contribution. Updated the contribution overview to reflect how to avoid that error when transitioning between steps 3 and 4 in `Your First Documentation Contribution`

Author: wouterj

contributing/documentation/overview.rst

@@ -107,6 +107,12 @@ your project:
     upstream  https://github.com/symfony/symfony-docs.git (fetch)
     upstream  https://github.com/symfony/symfony-docs.git (push)
 
+Fetch all the commits of the upstream branches by executing this command:
+
+.. code-block:: bash
+
+    $ git fetch upstream
+
 The purpose of this step is to allow you work simultaneously on the official
 Symfony repository and on your own fork. You'll see this in action in a moment.
 
@@ -208,6 +214,7 @@ contribution to the Symfony docs:
 
     # create a new branch based on the oldest maintained version
     $ cd projects/symfony-docs/
+    $ git fetch upstream
     $ git checkout -b my_changes upstream/2.7
 
     # ... do your changes