Documentation/mb/starlabs: De-duplicate the building instructions

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Change-Id: I20301b3041a62eb416ed61a84544ec4e5cc66c1e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68585
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/mainboard/starlabs/common/building.md

@@ -0,0 +1,30 @@
+## Building coreboot
+
+### Preliminaries
+
+Prior to building coreboot the following files are required:
+
+#### StarBook series:
+* Intel Flash Descriptor file (descriptor.bin)
+* Intel Management Engine firmware (me.bin)
+* ITE Embedded Controller firmware (ec.bin)
+
+#### StarLite series:
+* Intel Flash Descriptor file (descriptor.bin)
+* IFWI Image (ifwi.rom)
+
+The files listed below are optional:
+- Splash screen image in Windows 3.1 BMP format (Logo.bmp)
+
+These files exist in the correct location in the [StarLabsLtd/blobs](https://github.com/StarLabsLtd/blobs) repo on GitHub which is used in place of the standard 3rdparty/blobs repo.
+
+### Build
+
+The following commands will build a working image, where the last two words represent the
+series and processor i.e. `lite_glkr`:
+
+```bash
+make distclean
+make defconfig KBUILD_DEFCONFIG=configs/config.starlabs_starbook_adl
+make
+```