updated deployment action

used a version copied from another project (URL in source). 

one key change is the use of the `JamesIves/github-pages-deploy-action@3.7.1` action. in my previous attemps, this path looked like the name of the current repository, so i changed it to "connectuum/poemdown@main". now, however, it looks to me like this action is required -- it likely contains the steps/logic for deploying to GitHub Pages.

.github/workflows/main.yml

@@ -1,22 +1,44 @@
-name: Build and Deploy
-on: 
-    push:
-        branches: [ main ]
+# adapted from https://github.com/Swimburger/BlazorGitHubPagesDemo
+name: Deploy to GitHub Pages
+
+# Run workflow on every push to the main branch
+on:
+  push:
+    branches: [ main ]
+
 jobs:
-    build-and-deploy:
-        runs-on: ubuntu-latest    
-        steps:
-        - uses: actions/checkout@v2
-        - name: Setup .NET Core
-          uses: actions/setup-dotnet@v1
-          with:
-            dotnet-version: '6.0.x'
-        - name: Publish with dotnet
-          run: dotnet publish -c Release -o build --nologo
-        - name: Deploy to Github Pages
-          uses: connectuum/poemdown@main
-          with:
-            ACCESS_TOKEN: ${{ secrets.ACCESS_TOKEN }}
-            BASE_BRANCH: main
-            BRANCH: gh-pages
-            FOLDER: build/wwwroot
+  deploy-to-github-pages:
+    # use ubuntu-latest image to run steps on
+    runs-on: ubuntu-latest
+    steps:
+      # uses GitHub's checkout action to checkout code form the main branch
+      - uses: actions/checkout@v2
+
+      # sets up .NET Core SDK 3.1
+      - name: Setup .NET Core SDK
+        uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: 3.1
+
+      # publishes Blazor project to the release-folder
+      - name: Publish .NET Core Project
+        run: dotnet publish BlazorGitHubPagesDemo.csproj -c Release -o release --nologo
+
+      # changes the base-tag in index.html to match GitHub Pages repository subdirectory
+      - name: Change base-tag in index.html from / to /poemdown/
+        run: sed -i 's/<base href="\/" \/>/<base href="\/poemdown\/" \/>/g' release/wwwroot/index.html
+
+      # copy index.html to 404.html to serve the same file when a file is not found
+      - name: copy index.html to 404.html
+        run: cp release/wwwroot/index.html release/wwwroot/404.html
+
+      # add .nojekyll file to tell GitHub pages to not treat this as a Jekyll project. (Allow files and folders starting with an underscore)
+      - name: Add .nojekyll file
+        run: touch release/wwwroot/.nojekyll
+
+      - name: Commit wwwroot to GitHub Pages
+        uses: JamesIves/github-pages-deploy-action@3.7.1
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BRANCH: gh-pages
+          FOLDER: release/wwwroot