add pandoc

Author: dajmcdon

.github/workflows/R-CMD-check.yaml

@@ -15,6 +15,8 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - uses: r-lib/actions/setup-pandoc@v2
+
       - uses: r-lib/actions/setup-r@v2
         with:
           use-public-rspm: true