R1:ec22df5e171a

Update symbols docs

Summary: Refs T7977.

Test Plan: spellcheck.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7977

Differential Revision: https://secure.phabricator.com/D12688