doc request: add example of LowCardinality usage to example.go

[karelbilek]

I want to use ch-go to insert data with LowCardinality type.

I don't see any example how to do that. It would be enough to have that in the example.go.

[karelbilek]

What I did was to do

foo := (&proto.ColStr{}).LowCardinality()

That seems to have worked?

[zdyj3170101136]

var timestamp = new(chproto.ColDateTime).LowCardinality()