Update deploy docs re: OPPTools SalishSeaCast-prod branch

[douglatornell]

We are now maintaining our own branch in a fork on GitLab so that we can easily commit
changes for issues found in production rather than have them lying around as uncommitted
changes with worklog notes explaining them.

[codecov]

Codecov Report

Merging #98 (0c993d9) into main (dc059f6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #98   +/-   ##
=======================================
  Coverage   73.00%   73.00%           
=======================================
  Files         122      122           
  Lines       16068    16068           
  Branches     1308     1308           
=======================================
  Hits        11731    11731           
  Misses       4287     4287           
  Partials       50       50           

Flag	Coverage Δ
unittests	73.00% <ø> (ø)

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