Readme for dwave-networkx needs updating for other topologies (it only mentions Chimera)

[fionahanington]

Description
Readme for dwave-networkx needs updating for other topologies (it only mentions Chimera)

To Reproduce
Go to https://docs.ocean.dwavesys.com/en/stable/docs_dnx/sdk_index.html
or readme of this repo

Expected behavior
Should also mention Pegasus and Chimera in this sentence: "It provides tools for working with Chimera graphs and implementations of graph-theory algorithms on the D-Wave system and other binary quadratic model samplers."