Add FAQ entry for running Cassandra (#4867)
Add FAQ entry for running Cassandra (#4867)

* Add FAQ entry for running Cassandra

Addresses issue istio/istio#10053

* Making clear why default config does not work

* Removing numbering of subsections

* Removed one unnecessary line

* Addressing editorial corrections and removing a section

istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io