Add deployment documentation explaining GitHub Pages fix

Author: dataGriff

DEPLOYMENT.md

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+# Deployment Guide
+
+## GitHub Pages Deployment
+
+This presentation site is automatically deployed to GitHub Pages via GitHub Actions.
+
+### Why We Use `lib/` Instead of `node_modules/`
+
+GitHub Pages has restrictions on serving certain directories. The `node_modules` directory, even when included in Jekyll config, may not be reliably served. To fix this:
+
+1. **reveal.js files are copied to `lib/reveal.js/`** during build
+2. **All presentations reference `../../lib/reveal.js/`** instead of `../../node_modules/reveal.js/`
+3. **The build process automatically sets up the `lib` directory**
+
+### Build Process
+
+The GitHub Actions workflow:
+
+1. Installs dependencies with `npm ci`
+2. Runs `npm run build` which copies reveal.js files to `lib/`
+3. Deploys the site to GitHub Pages
+
+### Local Development
+
+For local development:
+
+```bash
+# Install dependencies and set up lib directory
+npm install
+
+# Start local server
+npm run serve
+
+# Or use the task runner
+task install
+task serve
+```
+
+### Creating New Presentations
+
+Use the task runner to create presentations:
+
+```bash
+task new -- my-presentation-name
+```
+
+This automatically creates presentations that use the correct `lib/reveal.js/` paths.
+
+### If You Get 404 Errors
+
+If presentations show 404 errors on GitHub Pages:
+
+1. Check that the `lib/` directory exists and contains reveal.js files
+2. Ensure presentations reference `../../lib/reveal.js/` paths
+3. Verify the GitHub Actions build completed successfully
+4. Check that `_config.yml` includes the `lib` directory
+
+### Manual Build
+
+To manually rebuild the lib directory:
+
+```bash
+npm run build
+# or
+task setup-lib
+```
+