Minhash token filter needs better documentation

[rpedela]

The Minhash Token Filter documentation only describes the interface for the token filter. That is fine for most token filters, but this one is more complicated.

1. It should list possible use cases such as an alternative to the "more like this" query.
2. It should talk about the recommended number of shingles: 5.
3. It should give small but complete examples for 1 and 2.

In the Lucene issue, they discuss Jaccard and cosine similarities. Did that make it into the final patch? If so, should that be exposed as a setting?

[clintongormley]

@rpedela I know nothing about it. Fancy sending a PR with the details?

[pkmital]

Also struggling to use this! Any help would be appreciated.

[romseygeek]

cc @elastic/es-search-aggs

[wayliew]

mark it