Add GitHub Actions CI

Author: purcell

.github/workflows/ci.yml

@@ -0,0 +1,30 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    paths-ignore:
+    - '**.md'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        emacs_version:
+          - 25.1
+          - 25.2
+          - 25.3
+          - 26.1
+          - 26.2
+          - 26.3
+          - 27.1
+          - snapshot
+    steps:
+    - uses: purcell/setup-emacs@master
+      with:
+        version: ${{ matrix.emacs_version }}
+
+    - uses: actions/checkout@v2
+    - name: Run tests
+      run: make check

README.md

@@ -1,3 +1,6 @@
+[![MELPA](https://melpa.org/packages/purescript-mode-badge.svg)](https://melpa.org/#/purescript-mode)
+[![Build Status](https://github.com/purescript-emacs/purescript-mode/workflows/ci/badge.svg)](https://github.com/purescript-emacs/purescript-mode/actions)
+
 PureScript Mode for Emacs
 ----------------------