SqlSetup: Update comment-based help in example

[johlju]

Pull Request (PR) description

• SqlSetup
  • The example 4-InstallNamedInstanceInFailoverClusterFirstNode.ps1 was
    updated to no longer reference the issue xSQLServerSetup: When doing cluster install the built-in PsDscRunAsCredential cannot be used #405 and issue xSQLServerSetup: When action is 'Addnode', the parameter 'PsDscRunAsCredential' must be used to login to the instance #444 in the
    comment-based help. The issues was fixed a while back and SqlSetup
    now supports the built-in parameter PsDscRunAsCredential (issue SqlSetup: Example referencing fixed issue #975).

This Pull Request (PR) fixes the following issues

• Fixes SqlSetup: Example referencing fixed issue #975

Task list

• Added an entry to the change log under the Unreleased section of the
  file CHANGELOG.md. Entry should say what was changed and how that
  affects users (if applicable), and reference the issue being resolved
  (if applicable).
• Resource documentation updated in the resource's README.md.
• Resource parameter descriptions updated in schema.mof.
• Comment-based help updated, including parameter descriptions.
• Localization strings updated.
• Examples updated.
• Unit tests updated. See DSC Community Testing Guidelines.
• Integration tests updated (where possible). See DSC Community Testing Guidelines.
• Code changes adheres to DSC Community Style Guidelines.

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This change is 

[codecov]

Codecov Report

Merging #1609 into master will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1609   +/-   ##
======================================
  Coverage      98%     98%           
======================================
  Files          37      37           
  Lines        5964    5963    -1     
======================================
  Hits         5874    5874           
+ Misses         90      89    -1     

Flag	Coverage Δ
#unit	98% <100%> (+<1%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
source/DSCResources/DSC_SqlSetup/DSC_SqlSetup.psm1	98% <100%> (+<1%)	⬆️
...DSC_SqlWindowsFirewall/DSC_SqlWindowsFirewall.psm1	100% <100%> (ø)
...dules/SqlServerDsc.Common/SqlServerDsc.Common.psm1	97% <100%> (+<1%)	⬆️

[johlju]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved