Add GitHub action to re-knit README.rmd whenever changes are pushed t…

…o it.

.github/workflows/render-README.yml

@@ -0,0 +1,23 @@
+on:
+  push:
+    paths:
+      - 'README.Rmd'
+
+jobs:
+  render:
+    name: Render README
+    runs-on: macOS-latest
+    env:
+      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: r-lib/actions/setup-r@v1
+      - uses: r-lib/actions/setup-pandoc@v1
+      - name: Install rmarkdown
+        run: Rscript -e 'install.packages("rmarkdown")'
+      - name: Render README
+        run: Rscript -e 'rmarkdown::render("README.Rmd", output_format = "md_document")'
+      - name: Commit results
+        run: |
+          git commit -m 'Re-build README.Rmd' || echo "No changes to commit"
+          git push origin || echo "No changes to commit"