Rename Bitcoin Cash to eCash in backporting instructions + minor fixes
Rename Bitcoin Cash to eCash in backporting instructions + minor fixes

Summary: Style fixes and a missed eCash rebrand

Test Plan: read

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11379

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