Add docs for MysqlFramework::Scripts::Table

[chrisbarber86]

Need to add usage examples for MysqlFramework::Scripts::Table in README file.

e.g.

class UsersTable
  extend MysqlFramework::Scripts::Table

  NAME = 'users'

  COLUMNS = [
    :id,
    :name,
    :email,
    :created_at,
    :updated_at
  ]

  def self.column_names
    COLUMNS.map { |c| "`#{NAME}`.`#{c}`" }.join(',')
  end

  def self.values
    COLUMNS.map { |c| '?' }.join(',')
  end

  register_table NAME
end