[#897] Report: favicon not showing on github pages (#898)

Modern browsers automatically try to load the favicon from the root of
the website.

However, for GitHub pages, our favicon is not located in the root but in
another path.

Let's explicitly add a link to our favicon resource so that it gets
displayed.

frontend/src/index.pug

@@ -1,6 +1,7 @@
 html
   head
     title RepoSense Report
+    link(rel="shortcut icon" type="image/x-icon" href="favicon.ico")
     link(rel="stylesheet", href="https://fonts.googleapis.com/css?family=Titillium+Web")
     link(rel="stylesheet", href="https://cdn.jsdelivr.net/npm/normalize.css@8.0/normalize.min.css")
     link(rel="stylesheet", href="https://cdn.jsdelivr.net/npm/muicss@0.9/dist/css/mui.min.css")