[Docs RFC] In add_dimension few of the multi-node references

[igor2x]

In add_dimension() page: https://docs.timescale.com/api/latest/hypertable/add_dimension/

• there are a few references to discontinued multi-node feature or
• specially mention single-node, that is now the only option.

Above paragraph was clearly written before v2.13 release when by_range was released. Consider writing suggestion, instead of using "space dimension" by_hash it may be more useful to use by_range (that is new feature in v2.13) to reduce the need for data reorder inside chunks.