add rule doc links to scores

[pq]

Adds doc links to rule names in the scorecard.

name	linter	dart sdk	fix	pedantic	flutter user	flutter repo	status	bug refs
always_declare_return_types	0.1.4	2.0.0				✅
always_put_control_body_on_new_line	0.1.31	2.0.0				✅
always_put_required_named_parameters_first	0.1.33	2.0.0
always_require_non_null_named_parameters	0.1.31	2.0.0	💡			✅
always_specify_types	0.1.4	2.0.0	💡			✅
annotate_overrides	0.1.11	2.0.0	💡			✅
avoid_annotating_with_dynamic	0.1.31	2.0.0	💡					dart-lang/sdk#57789
avoid_as	0.1.5	2.0.0				✅
avoid_bool_literals_in_conditional_expressions	0.1.46	2.0.0
avoid_catches_without_on_clauses	0.1.31	2.0.0
avoid_catching_errors	0.1.31	2.0.0
avoid_classes_with_only_static_members	0.1.31	2.0.0				✅
avoid_double_and_int_checks	0.1.47	2.0.0
avoid_empty_else	0.1.8	2.0.0	💡	✅	✅	✅
avoid_field_initializers_in_const_classes	0.1.48	2.0.0				✅

...

Full run here: dart-lang/sdk#57912

/cc @bwilkerson

[coveralls]

Coverage remained the same at 91.07% when pulling dc0bf54 on rule_links_for_scores into 0cade5d on master.