Add minimal example and associated helper functions

• Adds an example showing the simplest number of steps to run PE on GW150914
• Adds a helper (rapper) function to quickly get the BBH likelihood instance

@paul-lasky @colm.talbot @moritz.huebner what do you think? It seems a bit silly, but gets it down to 6 lines. If it is only used in Paul's talks then that's enough for me :)

added 1 commit

• f8cae1c4 - Add minimal example and associated helper functions

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This is nice, I'll merge it. Although I may change the last line to do more post-processing.

We should probably take that out of the sampler step anyway since it's likely to require tuning for each use case.

mentioned in commit 954b243e

merged