Add LinkedIn link to the navbar

Author: IanWitham

_includes/navbar.html

@@ -145,6 +145,9 @@
                             <a role="menuitem" class="group" href="https://www.reddit.com/r/fsharp/">
                                 <i class="fa-brands fa-reddit"></i> Reddit
                             </a>
+                            <a role="menuitem" class="group" href="https://www.linkedin.com/groups/13506105">
+                                <i class="fa-brands fa-linkedin"></i> LinkedIn
+                            </a>
                             <a role="menuitem" class="group" href="http://stackoverflow.com/questions/tagged/f%23">
                                 <i class="fa-brands fa-stack-overflow"></i> StackOverflow
                             </a>