Support auto-correction for Lint/ElseLayout

[koic]

This PR supports auto-correction for Lint/ElseLayout.

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Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

Looks good to me. We should probably clarify in the examples that's a lint cop, as often people type else when they meant elsif. The cop message makes that clear, but there's no example about this. We should also clarify the auto-correct assumes that we're facing a layout issue, not a logical issue.

[koic]

Certainly it is very valuable information! I updated the doc.

[bbatsov]

Great!