Add Discord join link to the community section

Discord server: "D Language Code Club"
previously known as "D Code Club" and "Wilds Code Club"

Author: 0xEAB

dlang.org.ddoc

@@ -260,6 +260,7 @@ $(SUBMENU_MANUAL
     $(SUBMENU_LINK $(ROOT_DIR)calendar.html, Calendar)
     $(SUBMENU_LINK_DIVIDER https://forum.dlang.org, Forums)
     $(SUBMENU_LINK irc://irc.freenode.net/d, IRC)
+    $(SUBMENU_LINK https://discord.gg/fva44g2, Discord)
     $(SUBMENU_LINK https://wiki.dlang.org, Wiki)
     $(SUBMENU_LINK_DIVIDER https://github.com/dlang, GitHub)
     $(SUBMENU_LINK $(ROOT_DIR)bugstats.html, Issues)