Fixed disclosure policy formatting

Summary: Mirrored to https://github.com/Bitcoin-ABC/bitcoinabc.org/pull/28

Test Plan: Read it

Reviewers: deadalnix, schancel, Fabien, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D2030