Change in coreboot[master]: Documentation: Add FIT payload documentation

[build bot (Jenkins) (Code Review)]

build bot (Jenkins) has posted comments on this change. ( https://review.coreboot.org/27253 )

Change subject: Documentation: Add FIT payload documentation
......................................................................

Patch Set 1: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/29465/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/75414/ : SUCCESS