Add Forgejo logo and markdown

frontend/public/custom/assets/forgejo.svg

+<svg viewBox="0 0 212 212" xmlns="http://www.w3.org/2000/svg">
+  <style type="text/css">
+    circle {
+      fill: none;
+      stroke: #000;
+      stroke-width: 15;
+    }
+    path {
+      fill: none;
+      stroke: #000;
+      stroke-width: 25;
+    }
+    .orange {
+      stroke:#ff6600;
+    }
+    .red {
+      stroke:#d40000;
+    }
+  </style>
+  <g transform="translate(6,6)">
+    <path d="M58 168 v-98 a50 50 0 0 1 50-50 h20" class="orange" />
+    <path d="M58 168 v-30 a50 50 0 0 1 50-50 h20" class="red" />
+    <circle cx="142" cy="20" r="18" class="orange" />
+    <circle cx="142" cy="88" r="18" class="red" />
+    <circle cx="58" cy="180" r="18" class="red" />
+  </g>
+</svg>

frontend/public/custom/markdown/forgejo.md

+---
+title: 'Forgejo'
+tileExcerpt: 'Software development tool and version control using Git, including bug tracking, code review, tickets and wikis'
+---
+
+## Introduction
+
+> [Forgejo](https://forgejo.org/) is a self-hosted lightweight software forge. Easy to install and low maintenance, it just does the job.
+
+## Signing in
+
+Forgejo shows some public data without requiring a sign-in. To sign in, first
+click "Sign in" in the top-right corner, then on the resulting Forgejo sign-in
+page click the organisation logo at the bottom saying "Sign in with".