Format all instructions.append.md to start with an H1 (required but ignored) and H2

[IsaacG]

See related discussions here as well as exercism/docs#592. Append files should all have an H1. Including an H2 helps break the flow from the non-append file to the append file so it does not read as the same stream of thought.

[github-actions]

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Automated comment created by PR Commenter 🤖.

[angelikatyborska]

I am assuming this is some sort of global platform change. Could you please provide a link to an explanation where this change is discussed and/or announced so I could familiarize myself? PRs with empty descriptions are confusing to maintainers that don't read whichever communications channel this was announced in.

[IsaacG]

Apologies. See related discussions here as well as exercism/docs#592