docs/user: slightly reword section on system calls

Expand the description slightly and quote ioctl(). I did ponder
mentioning something about why DRM ioctls are often missing but I see
we have the I915 ones so I guess its just no one has done them.

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20250725154517.3523095-5-alex.bennee@linaro.org>

docs/user/main.rst

@@ -20,10 +20,14 @@ QEMU user space emulation has the following notable features:
 System call translation
 ~~~~~~~~~~~~~~~~~~~~~~~
 
-QEMU includes a generic system call translator. This means that the
-parameters of the system calls can be converted to fix endianness
-and 32/64-bit mismatches between hosts and targets. IOCTLs can be
-converted too.
+System calls are the principle interface between user-space and the
+kernel. Generally the same system calls exist on all versions of the
+kernel so QEMU includes a generic system call translator. The
+translator takes care of adjusting endianess, 32/64 bit parameter size
+and then calling the equivalent host system call.
+
+QEMU can also adjust device specific ``ioctl()`` calls in a similar
+fashion.
 
 POSIX signal handling
 ~~~~~~~~~~~~~~~~~~~~~