doc/dev: add context note to dev guide config

This PR adds a note directing first-time cloners of
their Ceph git forks to make sure to cd into the ceph/
directory before trying to run the "git config" commands.

Signed-off-by: Zac Dover <zac.dover@gmail.com>

doc/dev/developer_guide/basic-workflow.rst

@@ -142,6 +142,10 @@ to work on the Ceph repository.".
 
 1. Configure your local git environment with your name and email address.  
 
+   .. note::
+      These commands will work only from within the ``ceph/`` directory
+      that was created when you cloned your fork.
+
    .. prompt:: bash $
 
       git config user.name "FIRST_NAME LAST_NAME"