doc: Update qemu-i486

This PR improves the qemu-i486 documentation.

Signed-off-by: Alan C. Assis <acassis@gmail.com>

Documentation/platforms/x86/qemu/boards/qemu-i486/index.rst

@@ -4,3 +4,46 @@ qemu-i486
 
 Port of NuttX to QEMU in i486 mode.  This port will also run on real i486
 hardware (Google the Bifferboard).
+
+QEMU
+====
+
+QEMU is a generic and open source machine emulator and virtualizer.
+
+QEMU Installation
+-----------------
+
+You can install QEMU for x86 on Linux Ubuntu this way::
+
+   $ sudo apt install qemu-system-x86
+
+Executing QEMU
+--------------
+
+Running QEMU with the generated ``nuttx.elf`` file::
+
+  $ qemu-system-i386 -cpu 486 -m 2 -kernel nuttx.elf -nographic
+
+Configuration
+=============
+
+Use the default configuration process::
+
+   $ ./tools/configure.sh qemu-i486:<configname>
+
+These are the available configurations:
+
+nsh
+---
+
+Enables the NuttShell for i486 emulated on QEMU.
+After running the QEMU command above with nuttx.elf you will see::
+
+   SeaBIOS (version 1.16.3-debian-1.16.3-2)
+
+   iPXE (https://ipxe.org) 00:03.0 CA00 PCI2.10 PnP PMM+0018AED0+00000000 CA00
+
+   Booting from ROM..
+   NuttShell (NSH) NuttX-12.13.0
+   nsh>
+