README.md in numo-openblas-0.2.2 vs README.md in numo-openblas-0.3.0

- old
+ new
@@ -1,14 +1,24 @@
 # Numo::OpenBLAS
 
-[![Build Status](https://travis-ci.org/yoshoku/numo-openblas.svg?branch=master)](https://travis-ci.org/yoshoku/numo-openblas)
+[![Build Status](https://github.com/yoshoku/numo-openblas/workflows/build/badge.svg)](https://github.com/yoshoku/numo-openblas/actions?query=workflow%3Abuild)
 [![Gem Version](https://badge.fury.io/rb/numo-openblas.svg)](https://badge.fury.io/rb/numo-openblas)
 [![BSD 3-Clause License](https://img.shields.io/badge/License-BSD%203--Clause-orange.svg)](https://github.com/yoshoku/suika/blob/master/LICENSE.txt)
 
 Numo::OpenBLAS downloads and builds [OpenBLAS](https://www.openblas.net/) during installation and
 uses that as a background library for [Numo::Linalg](https://github.com/ruby-numo/numo-linalg).
 
 ## Installation
+
+Building LAPACK included with OpenBLAS requires Fortran compiler.
+
+macOS:
+
+    $ brew install gfortran
+
+Ubuntu:
+
+    $ sudo apt-get install gfortran
 
 Add this line to your application's Gemfile:
 
 ```ruby
 gem 'numo-openblas'