Adding documentation badge and link.

README.md

@@ -26,6 +26,8 @@ pip install -r requirements.txt
 
 ### Documentation
 
+Documentation of the `pompy` API is available at [Read the Docs](https://pompy-docs.readthedocs.io/en/latest/).
+
 Two Jupyter notebooks showing examples of using the package are included in the repository root directory. The [`Farrell et al. (2002) example.ipynb`](Farrell%20et%20al.%20%282002%29%20example.ipynb) notebook file illustrates an example of using the `pompy` package to generate an animation of an odour plume using the simulation parameters described in Farrell et al. (2002) and includes keys to match the symbols used to define the parameter in the paper with the relevant `pompy` class attributes. The [`Demonstration.ipynb`](Demonstrations.ipynb) and accompanying module `pompy.demos` give several other examples of setting up plume models using `pompy` and visualising the simulations.
 
 The below script will generate a 20 second MP4 animation (see above for GIF version) of a generated plume with model parameters consistent with those proposed in the Farrell et al. (2002) paper.