Update doc/source/documentation.rst

Co-authored-by: Adrien Berchet <[email protected]>

doc/source/documentation.rst

@@ -36,7 +36,7 @@ To build documentation, go into project's ``doc`` folder.
     $ cd doc  # assuming that you start from the project's root.
 
 Make sure you have installed into your virtual environment libraries from `docs` extras:
-``pip install neurom[docs]``. The run the command in the ``doc`` folder:
+``pip install neurom[docs]``. Then run the command in the ``doc`` folder:
 
 .. code-block:: bash