automate pkgdown site build with github action

.Rbuildignore

@@ -11,3 +11,4 @@ figs/
 ^cran-comments.md$
 ^docs
 ^logo
+^\.github$

.github/.gitignore

@@ -0,0 +1 @@
+*.html

.github/workflows/pkgdown.yaml

@@ -0,0 +1,53 @@
+on:
+  push:
+    branches:
+      - main
+      - master
+
+name: pkgdown
+
+jobs:
+  pkgdown:
+    runs-on: ubuntu-latest
+    env:
+      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: r-lib/actions/setup-r@v1
+
+      - uses: r-lib/actions/setup-pandoc@v1
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get install libcurl4-openssl-dev libharfbuzz-dev libfribidi-dev
+
+      - name: Query dependencies
+        run: |
+          install.packages('remotes')
+          saveRDS(remotes::dev_package_deps(dependencies = TRUE), ".github/depends.Rds", version = 2)
+          writeLines(sprintf("R-%i.%i", getRversion()$major, getRversion()$minor), ".github/R-version")
+        shell: Rscript {0}
+
+      - name: Restore R package cache
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.R_LIBS_USER }}
+          key: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-${{ hashFiles('.github/depends.Rds') }}
+          restore-keys: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-
+
+      - name: Install dependencies
+        run: |
+          remotes::install_deps(dependencies = TRUE)
+          install.packages("pkgdown")
+        shell: Rscript {0}
+
+      - name: Install package
+        run: R CMD INSTALL .
+
+      - name: Deploy site to gh-pages branch
+        run: |
+          git config --local user.email "[email protected]"
+          git config --local user.name "GitHub Actions"
+          Rscript -e 'pkgdown::deploy_to_branch(new_process = FALSE)'
+