Merge pull request #4016 from Saxenauts/add_commit_dev_start

doc/dev_start_guide.txt

@@ -147,9 +147,13 @@ of the `master` branch (the principal one) of the central repository
 Submit your changes to the central repository
 ---------------------------------------------
 
-Once your code is ready for others to review, you need to push your
+Once your code is ready for others to review, you need to commit all the changes and then push your
 branch to your github fork first:
 
+.. code-block:: bash
+    
+    git commit -a -m "your message here"
+
 .. code-block:: bash
 
     git push -u origin my_shiny_feature