Add multi query documentation

[gabrieljaegerde]

There are currently examples for querying a single storage entry as well as querying all entries but there is no documentation on how to query the identities of 2 wallets together in one query for example.

I would assume this is currently possible (with query_map?) and an example in the docs would be much appreciated.

[arjanz]

Currently this isn't possible yet unfortunately, the query_map() is currently only retrieving all storage keys for provided storage function. But this wouldn't be much work to implement a new query_multi() function, that accepts a list of StorageKey objects, like the way subscibe_storage() works now.

I'll create and a PR later for this.

[gabrieljaegerde]

Perfect. 😄

[arjanz]

Released: https://github.com/polkascan/py-substrate-interface/releases/tag/v1.6.2

[gabrieljaegerde]

Thank you! 😄