Document how to include custom sortBy issue

[MoritzLost]

Description

I recently had some issues figuring out how to configure a custom sort parameter statically – without using the sortBy widget. As per this issue, the solution is to add the sort parameter directly to the index name (indexName: 'my_index:my_custom_param:asc'). This isn't documented anywhere as far as I can tell. It would be great to mention this in the README and provide examples for instantsearch-js as well as the InstantSearch libraries for React/Vue/etc.

[bidoubiwa]

Good idea! Thanks for the issue :)

[iarmankhan]

Thank you @MoritzLost Spent few hours trying to achieve the exact same thing and then stumbled upon this issue.
Strange that they never documented it :/

[bidoubiwa]

It should be added, I'm hoping someone has time to contribute to add that small piece of documentation.