JP-3534 update to Sky Match docs

[jemorrison]

Resolves JP-3534

Closes #8269

This PR addresses corrects the spelling of the parameter options 'usigma' and 'lsigma'.

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.35%. Comparing base (4cc0ac1) to head (d75c5c4).
Report is 23 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8356      +/-   ##
==========================================
+ Coverage   75.15%   75.35%   +0.20%     
==========================================
  Files         470      474       +4     
  Lines       38604    38944     +340     
==========================================
+ Hits        29014    29348     +334     
- Misses       9590     9596       +6     

Flag	Coverage Δ		*Carryforward flag
nightly	77.33% <ø> (-0.07%)	⬇️	Carriedforward from 4cc0ac1

*This pull request uses carry forward flags. Click here to find out more.

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[tapastro]

LGTM