Add last modified tag

Author: attilamester

Gemfile

@@ -9,3 +9,4 @@ git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 gem "jekyll", "~> 4.2"
 gem "jekyll-theme-slate"
 gem "webrick"
+gem "jekyll-last-modified-at"

_config.yml

@@ -1,3 +1,5 @@
 theme: jekyll-theme-slate
 # Google Analytics
-google_analytics: G-9BTS4G6VV4
+google_analytics: G-9BTS4G6VV4
+plugins:
+  - jekyll-last-modified-at

_layouts/default.html

@@ -19,6 +19,9 @@
               background: url("{{ site.baseurl }}/assets/images/icon-home.png") no-repeat 50% 50%;
               background-size: 90%;
               border: 3px solid white; border-radius: 50%; }
+
+    #lastmod { display: block; position: absolute; bottom: 10px; left: 10px; z-index: 10;
+              color: gray; font-size: 0.9em; font-weight: bold; font-family: Courier New; }
     </style>
 
 
@@ -57,6 +60,8 @@ <h2 id="project_tagline">{{ site.description | default: site.github.project_tagl
               <a class="tar_download_link" href="{{ site.github.tar_url }}">Download this project as a tar.gz file</a>
             </section>
           {% endif %}
+
+          <div id="lastmod">Updated: {{ page.last_modified_at | date: '%Y. %B %d.' }}</div>
         </header>
     </div>