qemu-options: Clarify handling of commas in options parameters

qemu-options: Clarify handling of commas in options parameters

Provide explicit guidance on dealing with option parameters as arbitrary
strings containing commas, such as in "file=my,file" and "string=a,b". The
updated documentation emphasizes the need to double commas when they
appear within such parameters.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1839
Signed-off-by: Yihuan Pan <xun794@gmail.com>
Message-ID: <20231213141706.629833-2-xun794@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>