README.md in convert_unit-0.1.0 vs README.md in convert_unit-0.2.0

@@ -1,9 +1,11 @@
 # ConvertUnit
 [![Build Status](https://travis-ci.org/tanvir002700/convert_unit.svg?branch=master)](https://travis-ci.org/tanvir002700/convert_unit)
 [![Coverage Status](https://coveralls.io/repos/github/tanvir002700/convert_unit/badge.svg?branch=master)](https://coveralls.io/github/tanvir002700/convert_unit?branch=master)
 [![Maintainability](https://api.codeclimate.com/v1/badges/6e3e7ff7c7b040d1680d/maintainability)](https://codeclimate.com/github/tanvir002700/convert_unit/maintainability)
+[![Gem Version](https://badge.fury.io/rb/convert_unit.svg)](https://rubygems.org/gems/convert_unit) 
+[![Downloads](https://img.shields.io/gem/dt/convert_unit.svg)](https://rubygems.org/gems/convert_unit)
 [![GitHub last commit (branch)](https://img.shields.io/github/last-commit/tanvir002700/convert_unit/master.svg)](https://github.com/tanvir002700/convert_unit)
 [![license](https://img.shields.io/github/license/tanvir002700/convert_unit.svg)](https://github.com/tanvir002700/convert_unit/blob/master/LICENSE)
 
 ## Introduction
 
@@ -41,11 +43,12 @@
 ConvertUnit::Length.new(1, 'km') === ConvertUnit::Length.new(1000, 'm') #=> false
 
 # Arithmetic
 ConvertUnit::Length.new(1, 'km') + ConvertUnit::Length.new(1, 'km') == ConvertUnit::Length.new(2, 'km')
 ConvertUnit::Length.new(1, 'km') + ConvertUnit::Length.new(1000, 'm') == ConvertUnit::Length.new(2, 'km')
-ConvertUnit::Length.new(1000, 'm') + ConvertUnit::Length.new(1, 'km') == ConvertUnit::Length.new(2, 'm')
+ConvertUnit::Length.new(1000, 'm') + ConvertUnit::Length.new(1, 'km') == ConvertUnit::Length.new(2000, 'm')
+ConvertUnit::Length.new(1000, 'm') - ConvertUnit::Length.new(1, 'km') == ConvertUnit::Length.new(0, 'm')
 
 # Valid units argument list
 ConvertUnit::Length::UNITS_SYMBOL       #=> { "millimeter"=>"mm", "centimeter"=>"cm", "meter"=>"m",
                                         #     "kilometer"=>"km", "inche"=>"in", "feet"=>"ft", "yard"=>"yd", 
                                         #     "mile"=>"mi" }
@@ -60,9 +63,12 @@
 :---------:|:------------------------------:
 Length     | mm, cm, m, km, in, ft, yd, mi
 Area       | mm2, cm2, m2, in2, ft2, yd2
 Mass       | g, kg, tonne, sh_ton, l_ton, lb, oz
 Volume     | cm3, m3, ltr, in3, ft3, us_gal, imp_gal, us_brl
+Density    | g/ml kg/m3 lb/ft3 lb/in3
+Volumetric Liquid flow | l/sec l/min m3 ft3/min ft3/hr gal/min brl/d
+Volumetric Liquid flow | nm3/hr scfh scfm
 ## Contributing
 
 Bug reports and pull requests are welcome on GitHub at https://github.com/tanvir002700/convert_unit. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org) code of conduct.
 See the [Contribution Guidelines](https://github.com/tanvir002700/convert_unit/blob/master/CONTRIBUTING.md)