Change in coreboot[master]: Documentation: Add Gigabyte to list of mainboards

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Change subject: Documentation: Add Gigabyte to list of mainboards
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Patch Set 3: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/29316/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/75257/ : SUCCESS