docs: add readme for how to start the Pub example (#1612)
docs: add readme for how to start the Pub example (#1612)

* docs: add readme for how to start the Pub example

* Apply suggestions from code review

Co-authored-by: Remi Rousselet <fa6a693dd9728de15f66edbe6c58e8e0cd3b01d9@gmail.com>
rrousselGit/river_pod,rrousselGit/river_pod,rrousselGit/river_pod,rrousselGit/river_pod