Adding document GitHub action

Author: gregorgorjanc

.github/workflows/.gitignore

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+*.html

.github/workflows/document.yaml

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+# Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
+# Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
+on:
+  push:
+    paths: ["R/**"]
+
+name: document.yaml
+
+permissions: read-all
+
+jobs:
+  document:
+    runs-on: ubuntu-latest
+    env:
+      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup R
+        uses: r-lib/actions/setup-r@v2
+        with:
+          use-public-rspm: true
+
+      - name: Install dependencies
+        uses: r-lib/actions/setup-r-dependencies@v2
+        with:
+          working-directory: RcppTskit
+          extra-packages: any::roxygen2
+          needs: roxygen2
+
+      - name: Document
+        run: setwd("RcppTskit"); roxygen2::roxygenise()
+        shell: Rscript {0}
+
+      - name: Commit and push changes
+        run: |
+          git config --local user.name "$GITHUB_ACTOR"
+          git config --local user.email "$GITHUB_ACTOR@users.noreply.github.com"
+          git add man/\* NAMESPACE DESCRIPTION
+          git commit -m "Update documentation" || echo "No changes to commit"
+          git pull --ff-only
+          git push origin