Add help info for channel joining and leaving.

demo/main.c

@@ -22,6 +22,8 @@
 
 void print_help() {
 	puts("Use `/' at the beginning to indicate a command (like in IRC).");
+	puts("  join         -- Join a channel (channel names start with `#').");
+	puts("  leave        -- Leave a channel (channel names start with `#').");
 	puts("  stats        -- Give network statistics of the local node.");
 	puts("  exit | quit  -- Close the program.");
 	puts("  help         -- Show this help information.");