Docs: Make Specific Rules docstring more user friendly

[jpy-git]

Brief summary of the change made

Follows on from discussion with @barrywhart here

Here's what the docs look like after updating the docstring:

Are there any other side effects of this change that we should be aware of?

No

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[barrywhart]

Tests failing due to network issue -- will probably work on a rerun.

[codecov]

Codecov Report

Merging #2241 (f1b7e9c) into main (91f8789) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main     #2241   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          156       156           
  Lines        11041     11041           
=========================================
  Hits         11041     11041           

Impacted Files	Coverage Δ
src/sqlfluff/core/rules/__init__.py	100.00% <ø> (ø)

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[jpy-git]

Tests failing due to network issue -- will probably work on a rerun.

yeah a re-run sorted things, will merge now 😄