flavours/linux: Add slirp to the list of recommend options

Oniro documentation recommends using of slirp option to have
network connection from/to the image in qemu. Adjust conf-notes.txt
to be consistent with the docs.

Signed-off-by: Pavel Zhukov <pavel.zhukov@huawei.com>

flavours/linux/conf-notes.txt

@@ -26,6 +26,6 @@ or via command line, e.g.:
 
 You can also run generated qemu images with a command:
 
-    $ runqemu qemux86-64 qemuparams="-nographic" oniro-image-base wic ovmf
+    $ runqemu qemux86-64 qemuparams="-nographic" oniro-image-base wic ovmf slirp
 
 Then log in as 'oniro' user with 'oniro' as a password.