User documentation: examples

[angus-g]

We have the capability for autogenerated documentation (that appears at https://lagrangian-filtering.readthedocs.io/en/latest/). I've already put installation instructions and some API documentation up, but I think the next useful thing would be worked examples.

[angus-g]

Here's an example that would be perfect for the documentation: analytic_example_v2.pdf

I'll have a look at whether this should be autogenerated from an examples folder, or other ways of getting an exported notebook available.