ci: basic github action for coverage (#537)

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,19 @@
-**Issue:** add link to pelletier/go-toml issue here
+<!--
+
+Thank you for your pull request!
+
+Please read the Code changes section of the CONTRIBUTING.md file,
+and make sure you have followed the instructions.
+
+https://github.com/pelletier/go-toml/blob/v2/CONTRIBUTING.md#code-changes
+
+-->
 
 Explanation of what this pull request does.
 
-More detailed description of the decisions being made and the reasons why (if the patch is non-trivial).
+More detailed description of the decisions being made and the reasons why (if
+the patch is non-trivial).
+
+---
+
+Paste `benchstat` results here

.github/workflows/coverage.yml

@@ -0,0 +1,23 @@
+name: coverage
+on:
+  push:
+    branches:
+      - v2
+  pull_request:
+    branches:
+      - v2
+
+jobs:
+  report:
+    runs-on: 'ubuntu-latest'
+    name: report
+    steps:
+      - uses: actions/checkout@master
+        with:
+          fetch-depth: 0
+      - name: Setup go
+        uses: actions/setup-go@master
+        with:
+          go-version: 1.16
+      - name: Run tests with coverage
+        run: ./ci.sh coverage -d "${GITHUB_BASE_REF-HEAD}"