README.qemu.md: fix markdown style issues

Fix markdown style issues using markdownlint tool [1]:

$ cat README.qemu.md | mdl
(stdin):8: MD006 Consider starting bulleted lists at the beginning of the line

[1] https://github.com/markdownlint/markdownlint
(From OE-Core rev: cf5f8f9ae809f3cc6a0d53bdfb28e6d913f2fecc)

Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

README.qemu.md

@@ -5,10 +5,10 @@ To simplify development, the build system supports building images to
 work with the QEMU emulator in system emulation mode. Several architectures
 are currently supported in 32 and 64 bit variants:
 
-  * ARM (qemuarm + qemuarm64)
-  * x86 (qemux86 + qemux86-64)
-  * PowerPC (qemuppc only)
-  * MIPS (qemumips + qemumips64)
+* ARM (qemuarm + qemuarm64)
+* x86 (qemux86 + qemux86-64)
+* PowerPC (qemuppc only)
+* MIPS (qemumips + qemumips64)
 
 Use of the QEMU images is covered in the Yocto Project Reference Manual.
 The appropriate MACHINE variable value corresponding to the target is given