Add CI action (#1)

* Create ci.yml

* Update README with CI status badge

.github/workflows/ci.yml

@@ -0,0 +1,18 @@
+name: CI
+
+on: [push]
+
+env:
+  DEVELOPER_DIR: /Applications/Xcode_11.1.app
+
+jobs:
+  build:
+
+    runs-on: macOS-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Build
+      run: |
+        set -o pipefail
+        xcodebuild build -scheme Calcifer -configuration Debug -sdk macosx | xcpretty -c

README.md

@@ -1,4 +1,6 @@
 # Calcifer 🔥
+[![Build status](https://github.com/simba909/calcifer/workflows/CI/badge.svg)](https://github.com/simba909/calcifer/actions)
+
 macOS menubar app for controlling external display brightness. Based on the great work in the [DDC.swift repo](https://github.com/reitermarkus/DDC.swift).
 
 ## Building from source