Adding in a workflow for generating API docs. Fixes #29 (#30)

.github/workflows/docs.yml

@@ -0,0 +1,24 @@
+name: Deploy docs
+
+on:
+  push:
+    branches: [master]
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    container:
+      image: crystallang/crystal:0.36.1
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          persist-credentials: false
+      - name: "Install shards"
+        run: shards install
+      - name: "Generate docs"
+        run: crystal docs
+      - name: Deploy to GitHub Pages
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./docs