fuchsia: Add beginning of build docs

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Bug: 706592
Change-Id: I7d18caed8ddb8c7c5d34f680d58a547c0516953e
Reviewed-on: https://chromium-review.googlesource.com/549056
Commit-Queue: Scott Graham <[email protected]>
Reviewed-by: Scott Graham <[email protected]>
Cr-Commit-Position: refs/heads/master@{#482340}
1 file changed