Docs - Minor update to Index page
Docs - Minor update to Index page

This patch addresses feedback regarding the `Installation` menu item on
the left-hand menu on the index page. That item has been relocated under
`Getting Started`. Additionally, the `Features` menu item has been
renamed `Overview`.

emccode/rexray,thecodeteam/rexray,akutz/rexray,oppodeldoc/rexray,emccode/rexray,oppodeldoc/rexray,akutz/rexray,cduchesne/rexray,ltouati/rexray,clintonskitson/rexray,emccode/rexray,codedellemc/rexray,codedellemc/rexray,cduchesne/rexray,emccode/rexray,akutz/rexray,ltouati/rexray,akutz/rexray,oppodeldoc/rexray,akutz/rexray,cduchesne/rexray,akutz/rexray,thecodeteam/rexray,codedellemc/rexray,cduchesne/rexray,oppodeldoc/rexray,clintonskitson/rexray,codedellemc/rexray,clintonskitson/rexray,thecodeteam/rexray,codedellemc/rexray,cduchesne/rexray,thecodeteam/rexray,oppodeldoc/rexray,oppodeldoc/rexray,cduchesne/rexray,ltouati/rexray,ltouati/rexray,codedellemc/rexray,thecodeteam/rexray,thecodeteam/rexray,clintonskitson/rexray