Write a cheat sheet or quickstart guide

The current quickstart guide is good at explaining what param is for but does not do a great job introducing users to some of the most important concepts.

I'd love to have some kind of cheat sheet or short primer on Param that covered some of the most important APIs that people still don't seem to know. That might include some of the most important methods:

- `inst.param.update()`: Setting multiple values
- `inst.param.values()`: Return a dict of values
- `inst.param.watch()`: Watch parameter(s) for changes
- `ParameterizedClass.parameter = 'default'`: Overriding default