* doc: added section on cluster hierarchy

* style: removed trailing whitespace in README

* style: removed fig legend info out of pre blocks

* doc: added section on service discovery

* doc: added assumption on number of replicas

* style: wrap text

* fix: typo in service discovery section

* fix: typo in service discovery section

* style: make variables in wikipedia quoted section italic

* doc: adds section on supported execution models

* doc: adds section on request routing in nodes in the README

* chore: added diagram link for partition control flow

* doc: adds section on partition replica controller, persistence mechanism and execution model