DOC better clarify upstream synchronization in contributing guide (#1…

…3505)

* clarify upstream synchronization

* apply Nicolas's comment

* fix typo

* don't mention the rebase

* move the notes

* fix branch name

doc/developers/contributing.rst

@@ -213,6 +213,22 @@ then submit a "pull request" (PR):
     and start making changes. Always use a ``feature`` branch. It's good practice to
     never work on the ``master`` branch!
 
+.. note::
+
+  In the above setup, your ``origin`` remote repository points to
+  ``YourLogin/scikit-learn.git``. If you wish to fetch/merge from the main
+  repository instead of your forked one, you will need to add another remote
+  to use instead of ``origin``. If we choose the name ``upstream`` for it, the
+  command will be::
+
+        $ git remote add upstream https://github.com/scikit-learn/scikit-learn.git
+
+  And in order to fetch the new remote and base your work on the latest changes
+  of it you can::
+
+        $ git fetch upstream
+        $ git checkout -b my-feature upstream/master
+
  6. Develop the feature on your feature branch on your computer, using Git to do the
     version control. When you're done editing, add changed files using ``git add``
     and then ``git commit`` files::
@@ -235,27 +251,18 @@ then submit a "pull request" (PR):
   If you are modifying a Cython module, you have to re-run step 4 after modifications
   and before testing them.
 
-.. note::
-
-  In the above setup, your ``origin`` remote repository points to
-  YourLogin/scikit-learn.git. If you wish to fetch/merge from the main
-  repository instead of your forked one, you will need to add another remote
-  to use instead of ``origin``. If we choose the name ``upstream`` for it, the
-  command will be::
-
-        $ git remote add upstream https://github.com/scikit-learn/scikit-learn.git
 
 If any of the above seems like magic to you, then look up the `Git documentation
 <https://git-scm.com/documentation>`_ and the `Git development workflow
 <http://docs.scipy.org/doc/numpy/dev/gitwash/development_workflow.html>`_ on the
 web, or ask a friend or another contributor for help.
 
 If some conflicts arise between your branch and the ``master`` branch, you need
-to merge ``master``. The command will be::
-
-  $ git merge master
+to merge ``master``. For that, you first need to fetch the ``upstream``, and
+then merge its ``master`` into your branch::
 
-with ``master`` being synchronized with the ``upstream``.
+  $ git fetch upstream
+  $ git merge upstream/master
 
 Subsequently, you need to solve the conflicts. You can refer to the `Git
 documentation related to resolving merge conflict using the command line