adding guidelines for minimum hardware requirements to install

guide.
As these next three items all have the same supported operating systems, what about consolidating them into one?

Such as:

Supported Operating Systems
...........................
Continuuity Loom has been tested against these platforms:

 * CentOS 6.4
 * Ubuntu 12.04

Supported Databases
...................
Continuuity Loom has been tested with databases:

 * Derby (default)
 * MySQL version 5.1 or above
 * Oracle DB
 * SQLite
 * PostgreSQL version 8.4 or above

Supported Zookeeper Versions
............................
Continuuity Loom has been tested with these versions of Zookeeper:

 * Apache Zookeeper version 3.4 or above
 * CDH4 or CDH5 Zookeeper
 * HDP1 or HDP2 Zookeeper