Client documentation is available on hex.pm.
How to use:
iex(1)> {:ok, client} = Gel.start_link() # NOTE: you should initialize Gel project first
iex(2)> arg = [16, 13, 2, 42]
iex(3)> ^arg = Gel.query_required_single!(client, "select <array<int64>>$arg", arg: arg)
[16, 13, 2, 42]