docs: fix description of gnpy-path-request
docs: fix description of gnpy-path-request

Since about f9e0d18 and 94a8f35, we've changed the way how the equipment
config (and also the network topology) is passed around. Update the
README to reflect this.

Change-Id: I338b790fd4d54914c49e5e0aac3f44f2bc9d00ee

Telecominfraproject/gnpy