Add test workflow on push to master

Add badge in README.

.github/workflows/test.yml

@@ -0,0 +1,22 @@
+name: test
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  run_tests:
+    runs-on: macos-11
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+      - uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: latest-stable
+      - name: Run tests
+        run: |
+          swift test

.ruby-version

@@ -0,0 +1 @@
+2.7

README.md

@@ -1,6 +1,7 @@
 ![iOS 11+](https://img.shields.io/badge/ios-11+-green.svg)
 ![macOS 10.15+](https://img.shields.io/badge/macos-10.15+-green.svg)
 [![License GPLv3](https://img.shields.io/badge/license-GPLv3-lightgray.svg)](LICENSE)
+[![GitHub Actions](https://github.com/passepartoutvpn/tunnelkit/actions/workflows/test.yml/badge.svg)](https://github.com/passepartoutvpn/tunnelkit/actions/workflows/test.yml)
 
 # TunnelKit