ci: set up linter

Author: quoid

.github/workflows/ci.yml

@@ -0,0 +1,13 @@
+name: CI
+on:
+  - push
+  - pull_request
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install modules
+      run: yarn
+    - name: Run ESLint
+      run: yarn run eslint . --ext .js,.jsx,.ts,.tsx