Update ard_hierarchical() denominator argument description

[edelarua]

What changes are proposed in this pull request?

• Updated denominator argument description for ard_hierarchical().

I copied over the description from ard_stack_hierarchical() with some minor modifications.

Closes #372

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[github-actions]

Unit Tests Summary

  1 files  180 suites   51s ⏱️
177 tests 177 ✅ 0 💤 0 ❌
435 runs  435 ✅ 0 💤 0 ❌

Results for commit fe5847b.

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[github-actions]

Unit Test Performance Difference

Additional test case details

Test Suite	$Status$	Time on main	$±Time$	Test Case
add_calculated_row	💔	$0.19$	$+1.11$	add_calculated_row_x_
ard_continuous	💚	$4.19$	$-3.95$	ard_continuous_works
ard_hierarchical	💔	$8.16$	$+1.17$	ard_hierarchical_works_without_by_variables
ard_strata	💔	$0.84$	$+2.14$	ard_strata_works

Results for commit a7b2ea5

♻️ This comment has been updated with latest results.