docs: add GitHub Pages deployment guide (#155)

Author: acrogenesis

README.md

@@ -71,6 +71,7 @@ Documentation can be found at <https://hexdocs.pm/tableau>.
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 ## Getting Started
 

guides/deploying-to-github-pages.md

@@ -0,0 +1,114 @@
+# Deploying to GitHub Pages
+
+GitHub Pages can host the static files that Tableau produces. This guide walks through a production-ready setup that you can adopt for your own site.
+
+## Prepare your Tableau project
+
+1. Set the production `url` in `config/prod.exs` (your custom domain or the full GitHub Pages URL):
+
+   ```elixir
+   # config/prod.exs
+   config :tableau, :config,
+     url: "https://your-domain.tld"
+   ```
+
+2. If you serve additional assets (Tailwind, esbuild, etc.), add the corresponding Mix tasks to the `build` alias so they also run in CI.
+
+## Add the GitHub Pages workflow
+
+Create `.github/workflows/deploy.yml` with the following workflow. It installs Erlang/OTP + Elixir, builds the site in production mode, and publishes the `_site` directory to GitHub Pages:
+
+```yaml
+name: Deploy site to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Erlang/OTP and Elixir
+        uses: erlef/setup-beam@v1
+        with:
+          otp-version: "28"
+          elixir-version: "1.18"
+
+      - name: Cache Mix deps
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.mix
+            deps
+            _build
+          key: ${{ runner.os }}-otp-28-elixir-1.18-mix-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-otp-28-elixir-1.18-mix-
+
+      - name: Install dependencies
+        run: MIX_ENV=prod mix deps.get --only prod
+
+      - name: Build site
+        run: MIX_ENV=prod mix build
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v4
+        with:
+          path: _site
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - id: deployment
+        uses: actions/deploy-pages@v4
+```
+
+### Workflow notes
+
+- Set `otp-version` and `elixir-version` to match your project.
+- Update the cache key when you bump OTP or Elixir so a fresh build occurs.
+- If `mix build` already chains your asset pipelines, no other changes are needed. Otherwise, insert additional steps before "Upload artifact".
+- The cache step speeds up successive runs but can be removed if you prefer.
+
+## Enable GitHub Pages
+
+1. Push the workflow to your default branch (the example uses `main`).
+2. In your repository, open **Settings → Pages**.
+3. Under **Build and deployment**, choose **GitHub Actions**.
+4. After the first successful run, the deployment will appear under the **Deployments** tab and the workflow output prints the public URL.
+
+## Custom domains & pages.io URLs
+
+If you have a custom domain:
+
+- Add a `CNAME` file at the repo root containing the domain, e.g. `example.com`.
+- Configure your DNS to point at GitHub Pages.
+- Keep `config :tableau, :config, url: "https://your-domain"` in sync so absolute links are generated correctly.
+- GitHub’s docs cover the DNS details in depth: <https://docs.github.com/en/pages/configuring-a-custom-domain-for-your-github-pages-site/about-custom-domains-and-github-pages>.
+
+If you deploy to `<user>.github.io/<repo>`, use the full Pages URL (e.g. `https://username.github.io/my-site`) and optionally set `base_path: "/my-site"` in `config/prod.exs` so local links match production.
+
+## Troubleshooting
+
+- See a 404 for nested routes? Double-check `base_path` in `config/prod.exs` when deploying under a subdirectory.
+- Need to rebuild assets? Append those build steps to the `build` alias so `mix build` runs everything locally and in CI.
+- Want to test locally? Run `MIX_ENV=prod mix build` and inspect the output directory (which defaults to  `_site/`) before pushing.
+
+With these pieces in place, every push to `main` rebuilds your Tableau site and deploys it to GitHub Pages.

mix.exs

@@ -67,6 +67,13 @@ defmodule Tableau.MixProject do
   defp docs do
     [
       main: "Tableau",
+      extras: [
+        "README.md",
+        "guides/deploying-to-github-pages.md"
+      ],
+      groups_for_extras: [
+        Guides: ~r/guides\/[^\/]+\.md/
+      ],
       groups_for_modules: [
         Site: [
           Tableau,