add simple contribution guide

Gemfile

@@ -9,6 +9,7 @@ group :development do
 end
 
 group :test do
+  gem 'rexml', '~> 3.2', '>= 3.2.4'
   gem 'minitest', '~> 5.14', require: 'minitest/autorun'
   gem 'minitest-reporters', '~> 1.4'
   gem 'mocha', '~> 1.11', require: 'mocha/minitest'

Gemfile.lock

@@ -27,6 +27,7 @@ GEM
       pry (~> 0.13.0)
     public_suffix (4.0.6)
     rake (13.0.1)
+    rexml (3.2.5)
     ruby-progressbar (1.10.1)
     simplecov (0.19.1)
       docile (~> 1.1)
@@ -47,6 +48,7 @@ DEPENDENCIES
   mocha (~> 1.11)
   pry-byebug
   rake (~> 13.0)
+  rexml (~> 3.2, >= 3.2.4)
   simplecov (~> 0.19)
   webmock (~> 3.10)
 

README.md

@@ -63,7 +63,7 @@ If you're using an Enterprise account, you can call the `gh-host <host>` command
 You can submit your bug reports or feature requests at:
 https://github.com/edgarjs/alfred-github-repos/issues
 
-If you want to submit a Pull Request, please follow these simple guides:
+If you want to submit a Pull Request, please read [CONTRIBUTING](./docs/CONTRIBUTING.md) then follow these simple guides:
 
 1. Add a detailed description of what you're changing and why.
 2. Add necessary unit tests that cover your changes.

docs/CONTRIBUTING.md

@@ -0,0 +1,13 @@
+# Run tests
+
+```sh
+rbenv global 3.0.6
+bundle install
+bundle exec rake
+```
+
+# Make Alfred package
+
+```sh
+./bin/package
+```