Add a workflow to publish on tag (#26)

Author: Mike Elsmore

.github/workflows/publish-to-crates.yml

@@ -0,0 +1,24 @@
+on:
+    push:
+      # Pattern matched against refs/tags
+      tags:        
+        - '*'           # Push events to every tag not containing /
+    workflow_dispatch:
+  name: Publish
+  jobs:
+    publish:
+      name: Publish
+      runs-on: ubuntu-latest
+      steps:
+        - name: Checkout sources
+          uses: actions/checkout@v2
+  
+        - name: Install stable toolchain
+          uses: actions-rs/toolchain@v1
+          with:
+            profile: minimal
+            toolchain: stable
+            override: true
+        - run: cargo publish --token ${CRATES_TOKEN}
+          env:
+            CRATES_TOKEN: ${{ secrets.CRATES_TOKEN }}