Add example how to install MySQL 5.6 on CentOS 7 (#931)

* Update READMe.md with example how to install MySQL Community Server 5.6 on Centos 7.3
This minimal example shows how to install MySQL Community Server 5.6 on Centos 7.3 using Puppet 3.8.7 using hiera.

Author: nvtkaszpir

README.md

@@ -320,6 +320,67 @@ Class['apt::update'] ->
 Class['::mysql::client']
 ```
 
+### Install MySQL Community server on CentOS
+
+You can install MySQL Community Server on CentOS using the mysql module and Hiera. This example was tested with the following versions:
+
+* MySQL Community Server 5.6
+* Centos 7.3
+* Puppet 3.8.7 using hiera
+* puppetlabs-mysql module v3.9.0
+
+In Puppet:
+
+```puppet
+  include ::mysql::server
+
+  create_resources(yumrepo, hiera('yumrepo', {}))
+
+  Yumrepo['repo.mysql.com'] -> Anchor['mysql::server::start']
+  Yumrepo['repo.mysql.com'] -> Package['mysql_client']
+
+  create_resources(mysql::db, hiera('mysql::server::db', {}))
+```
+
+In Hiera:
+
+```yaml
+---
+# mysql module requires feeding it a bunch of parameters to properly install MySQL, instead of MariaDB
+# Centos 7.3
+yumrepo:
+  'repo.mysql.com':
+    baseurl: "http://repo.mysql.com/yum/mysql-5.6-community/el/%{::operatingsystemmajrelease}/$basearch/"
+    descr: 'repo.mysql.com'
+    enabled: 1
+    gpgcheck: true
+    gpgkey: 'http://repo.mysql.com/RPM-GPG-KEY-mysql'
+
+mysql::client::package_name: "mysql-community-client" # required for proper MySQL installation
+mysql::server::package_name: "mysql-community-server" # required for proper MySQL installation
+mysql::server::package_ensure: 'installed' # do not specify version here, unfortunately yum fails with error that package is already installed
+mysql::server::root_password: "change_me_i_am_insecure"
+mysql::server::manage_config_file: true
+mysql::server::service_name: 'mysqld' # required for puppet module
+mysql::server::override_options:
+  'mysqld':
+    'bind-address': '127.0.0.1'
+    'log-error': /var/log/mysqld.log' # required for proper MySQL installation
+  'mysqld_safe':
+    'log-error': '/var/log/mysqld.log'  # required for proper MySQL installation
+
+# create database + account with access, passwords are not encrypted
+mysql::server::db:
+  "dev":
+    user: "dev"
+    password: "devpass"
+    host: "127.0.0.1"
+    grant:
+      - "ALL"
+
+```
+
+
 ## Reference
 
 ### Classes