Add Github action for RSpec tests

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby-version: ['2.7', '3.0']
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+    # To automatically get bug fixes and new Ruby versions for ruby/setup-ruby,
+    # change this to (see https://github.com/ruby/setup-ruby#versioning):
+    # uses: ruby/setup-ruby@v1
+      uses: ruby/setup-ruby@473e4d8fe5dd94ee328fdfca9f8c9c7afc9dae5e
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+    - name: Run tests
+      run: bundle exec rake

README.md

@@ -1,3 +1,5 @@
+[![Build Status](https://github.com/lacepool/nftmaker_api/workflows/CI/badge.svg?branch=main)](https://github.com/lacepool/nftmaker_api/actions)
+
 # NftmakerApi
 
 A Ruby client for the https://nft-maker.io/pro API.