Adds documentation to annotations as they are often misunderstood
Adds documentation to annotations as they are often misunderstood

Instrumentation libraries almost always get some aspect of annotations
wrong. This is an attempt to document them, so that folks have a better
chance at creating portable implementations.

Signed-off-by: Vladimir Kostyukov <vkostyukov@twitter.com>

RB_ID=759633

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