Add a GitHub Workflow to do Pandoc conversion (cabforum#234)

This builds the BRs, the EVGs, and the NSRs via GitHub Actions. However,
all of these are expected to fail at present, as further adjustments are
needed to each which will need to be balloted.

.github/workflows/build-draft-docs.yml

@@ -0,0 +1,29 @@
+name: Build Draft Guidelines
+on: [push, pull_request]
+jobs:
+  build_brs:
+    strategy:
+      matrix:
+        document:
+          - 'BR.md'
+          - 'EVG.md'
+          - 'NSR.md'
+    name: Build ${{ matrix.document }}
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - uses: cabforum/build-guidelines-action@v1.0.0-rc4
+        with:
+          markdown-file: docs/${{ matrix.document }}
+          pdf: true
+          docx: true
+          lint: true
+          draft: true
+      - uses: actions/upload-artifact@v2
+        with:
+          name: Converted ${{ matrix.document }}
+          path: |
+            docs/*.pdf
+            docs/*.docx
+          if-no-files-found: 'error'
+          retention-days: 21