update installation instructions for latest version (ytti#1383)

README.md

@@ -79,30 +79,32 @@ Check out the [Oxidized TREX 2014 presentation](http://youtu.be/kBQ_CTUuqeU#t=3h
 Install all required packages and gems.
 
 ```shell
-apt-get install ruby ruby-dev libsqlite3-dev libssl-dev pkg-config cmake libssh2-1-dev libicu-dev
+apt-get install ruby ruby-dev libsqlite3-dev libssl-dev pkg-config cmake libssh2-1-dev libicu-dev zlib1g-dev
 gem install oxidized
 gem install oxidized-script oxidized-web # if you don't install oxidized-web, make sure you remove "rest" from your config
 ```
 
 ### CentOS, Oracle Linux, Red Hat Linux
 
-On CentOS 6 / RHEL 6, install Ruby 2.0 or greater (for Ruby 2.1.2 installation instructions see [Installing Ruby 2.1.2 using RVM](#installing-ruby-212-using-rvm)), then install Oxidized dependencies
+On CentOS 6 / RHEL 6, begin by installing Ruby 2.0 or greater. For Ruby 2.1.2 installation instructions see [Installing Ruby 2.1.2 using RVM](#installing-ruby-212-using-rvm).
+
+If you've installed Ruby 2.0 or greater via a 3rd party package rather than the RVM instructions, additional dependencies will be required:
 
 ```shell
-yum install cmake sqlite-devel openssl-devel libssh2-devel libicu-devel
+yum install make cmake which sqlite-devel openssl-devel libssh2-devel ruby gcc ruby-devel libicu-devel gcc-c++
 ```
 
 RHEL 7 / CentOS 7 will work out of the box with the following package list:
 
 ```shell
-yum install cmake sqlite-devel openssl-devel libssh2-devel ruby gcc ruby-devel libicu-devel gcc-c++
+yum install make cmake which sqlite-devel openssl-devel libssh2-devel ruby gcc ruby-devel libicu-devel gcc-c++
 ```
 
 Now let's install oxidized via Rubygems:
 
 ```shell
 gem install oxidized
-gem install oxidized-script oxidized-web
+gem install oxidized-script oxidized-web # if you don't install oxidized-web, make sure you remove "rest" from your config
 ```
 
 ### FreeBSD
@@ -218,7 +220,7 @@ Install Ruby 2.1.2 build dependencies
 ```shell
 yum install curl gcc-c++ patch readline readline-devel zlib zlib-devel
 yum install libyaml-devel libffi-devel openssl-devel make cmake
-yum install bzip2 autoconf automake libtool bison iconv-devel libssh2-devel
+yum install bzip2 autoconf automake libtool bison iconv-devel libssh2-devel libicu-devel
 ```
 
 Install RVM