feat(readme)!: fix markdownlint violations

[felipecrs]

This fixes many markdownlint violations found in the generated docs.

[salesforce-cla[bot]]

Thanks for the contribution! Before we can merge this, we need @felipecrs to sign the Salesforce.com Contributor License Agreement.

[felipecrs]

Circle CI is failing due to a PGP error, I believe it has nothing to do with this PR.

https://app.circleci.com/pipelines/github/oclif/dev-cli/398/workflows/ba4e23fc-0aa5-4c47-a826-bc2d2967f64a/jobs/2032/parallel-runs/0/steps/0-105

[RasPhilCo]

@felipecrs thanks for the PR! However, we don't use markdownlint in this project. Likewise, markdownlint doesn't define a spec/standard.

[felipecrs]

Despite that, I don't believe there is any drawback of applying this PR.

[felipecrs]

I actually need it, because the way it works today, the hierarchy of the titles and subtitles in the .md files are not being correctly detected in Docusaurus for example (when using multi md files for each command).

[RasPhilCo]

Gotcha. We have a major bump for this package scheduled soon, we'll include it there.