Address high throughput reads/write needs in dist data modeling section

## Communication goals (e.g. detailed howto vs orientation)

Citus can act as "better NoSQL," handling high throughput reads and writes. Add an example to the dist data modeling section that illustrates how this works. We want to be sure people with this use case understand it is quite possible in Citus.

### Good locations for content in docs structure

New "Updatable Large Table" example in https://docs.citusdata.com/en/latest/sharding/data_modeling.html#typical-real-time-schemas

## How does this work? (devs)

### Example sql

### Corner cases, gotchas

### Are there relevant blog posts or outside documentation about the concept/feature?

https://www.citusdata.com/blog/2016/09/22/announcing-citus-mx/