Add commented-out option to weston.ini to set Xwayland path

User can remove the comment marks to make xwayland.so use a local
installed Xwayland server.
diff --git a/weston.ini.in b/weston.ini.in
index 06b51df..dff9e94 100644
--- a/weston.ini.in
+++ b/weston.ini.in
@@ -66,3 +66,6 @@
 
 [screen-share]
 command=@bindir@/weston --backend=rdp-backend.so --shell=fullscreen-shell.so --no-clients-resize
+
+#[xwayland]
+#path=@bindir@/Xwayland