baremetrics: Update documentation for current style/structure of integration docs.

[hanyucrocks]

Update the documentation for the baremetrics bot integration for the current style and structure of integration documentation pages.

See #871 and #867 for examples of the expectations for integration documentation style and structure.

This was noticed while reviewing zulip/zulip#38585, which
adds Baremetrics to the integrations catalog and depends on this doc being in good shape.

[hanyucrocks]

@laurynmm, tagging you for your visibility here. I am working on this issue as said on the CZO Thread.

[hanyucrocks]

@zulipbot add "bug" "help wanted"

[hanyucrocks]

@zulipbot claim

[zulipbot]

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