Added missing release notes for 0.19
Added missing release notes for 0.19

Summary: See title

Test Plan: Read it.

Reviewers: deadalnix, Fabien, Mengerian, #bitcoin_abc, markblundeberg

Reviewed By: deadalnix, #bitcoin_abc, markblundeberg

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2563

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