Updating Parcels pitch in readme

As we move towards v4, I feel it's time to say goodbye to the funny bacronym for Parcels. We don't use it anymore on the revamped oceanparcels.org website, and when we remove it here in the readme it will be gone from the codebase too.

I also aligned the pitch with that on the oceanparcels website

Author: erikvansebille

docs/index.rst

@@ -2,7 +2,7 @@ Parcels documentation
 =====================
 
 
-Welcome to the documentation of Parcels. **Parcels** (Probably A Really Computationally Efficient Lagrangian Simulator) is a set of Python classes and methods to create customisable particle tracking simulations using output from Ocean Circulation models. Parcels can be used to track passive and active particulates such as water, plankton, `plastic <http://www.topios.org/>`_ and `fish <https://github.com/Jacketless/IKAMOANA>`_.
+Welcome to the documentation of Parcels. **Parcels** provides a set of Python classes and methods to create customisable particle tracking simulations using gridded output from (ocean) circulation models. Parcels can be used to track passive and active particulates such as water, plankton, `plastic <http://www.topios.org/>`_ and `fish <https://github.com/Jacketless/IKAMOANA>`_.
 
 .. figure:: _static/homepage.gif
    :class: dark-light