Update index.xhtml.

src/index.xhtml

@@ -50,6 +50,7 @@
                     <li><b>Matrix messenger:</b> @Eisfunke:matrix.org</li>
                     <li><b>Telegram messenger:</b> @Eisfunke</li>
                     <li><b>Signal messenger:</b> Available</li>
+                    <li><b>Briar messenger:</b> Available</li>
                     <li><b>Steam:</b> <a href="https://steamcommunity.com/id/eisfunke">Eisfunke</a></li>
                 </ul>
             </div>
@@ -63,8 +64,8 @@
                 <h2>Involvements</h2>
                 <ul>
                     <li><b><a href="https://foss-ag.de">FOSS-AG</a>:</b> An organization of students enjoying and promoting Free and Open-Source Software.<br/></li>
-                    <li><b><a href="https://fsinfo.cs.tu-dortmund.de/fsr/start">FSR Informatik</a>:</b> The student representatives for computer science at the TU Dortmund.<br/></li>
-                    <li>Tutor for Functional Programming at Lehrstuhl 1 at the TU Dortmund.</li>
+                    <li><b><a href="https://fsinfo.cs.tu-dortmund.de/fsr/start">FSR Informatik</a>:</b> Chairman of the student representatives for computer science at TU Dortmund.<br/></li>
+                    <li>Tutor for Operating Systems at Lehrstuhl 12 at TU Dortmund.</li>
                 </ul>
             </div>