docs: Recommend slirp option for runqemu

With default network settings of runqemu script Oniro images start without
IP address assigned which may cause inconvenience for some users.
Using user network allows network access from the Oniro VM and
enables port forwarding for ssh access.

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

docs/build-flavours/linux-flavour.rst

@@ -39,7 +39,7 @@ You can test the image built for the qemux86-64 target by issuing:
 
 .. code-block:: console
 
-    $ runqemu qemux86-64 oniro-image-base wic ovmf
+    $ runqemu qemux86-64 oniro-image-base wic ovmf slirp
 
 After successful bootup, you will be dropped into a login shell:
 

docs/hardware-support/virtual-boards/qemux86-64.rst

@@ -48,4 +48,4 @@ Once the image is done, you can run the Qemu using the provided script wrapper:
 
 .. code-block:: console
 
-   $ MACHINE=qemux86-64 runqemu oniro-image-base wic ovmf
+   $ MACHINE=qemux86-64 runqemu oniro-image-base wic ovmf slirp

docs/hardware-support/virtual-boards/qemux86.rst

@@ -48,4 +48,4 @@ Once the image is done, you can run the Qemu using the provided script wrapper:
 
 .. code-block:: console
 
-   $ MACHINE=qemux86 runqemu oniro-image-base wic ovmf
+   $ MACHINE=qemux86 runqemu oniro-image-base wic ovmf slirp

docs/oniro-quick-build.rst

@@ -84,7 +84,7 @@ Once the image is built, you can run a Qemu X86-64 instance using the provided s
 
 .. code-block:: console
 
-      $ MACHINE=qemux86-64 runqemu oniro-image-base wic ovmf
+      $ MACHINE=qemux86-64 runqemu oniro-image-base wic ovmf slirp
 
 If the host has a VT-capable CPU, you can pass the ``kvm`` argument for better
 performance. Check ``runqemu``'s help message for all available arguments.