(JP 3158 ) Update docs for calwebb_detector1

[dmggh]

Resolves JP-3158

Closes #

This PR address updates the calwebb_detector1 documentation to include the undersampling correction step.
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

Patch and project coverage have no change.

Comparison is base (af63faf) 77.49% compared to head (516e1ce) 77.49%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7510   +/-   ##
=======================================
  Coverage   77.49%   77.49%           
=======================================
  Files         452      452           
  Lines       36193    36193           
=======================================
  Hits        28047    28047           
  Misses       8146     8146           

Flag	Coverage Δ		*Carryforward flag
nightly	77.47% <ø> (ø)		Carriedforward from af63faf

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

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[hbushouse]

Code updates look good and docs built from the PR are also good.