[7.10] docs: Update field ref with ECS icon (#4272)#4279

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bmorelli25 merged 1 commit intoelastic:7.10from bmorelli25:backport/7.10/pr-4272

Oct 7, 2020

+134-1

Commits on Oct 7, 2020

docs: Update field ref with ECS icon (elastic#4272 )
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