Modify installation.rst file to update UPP website link

[hertneky]

Update UPP website link in 2 places from DTC to EPIC owned website.

Expected Differences

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  
  If yes, please describe:
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  
  If yes, please describe:
  

Pull Request Testing

• Describe testing already performed for these changes:
  
  None

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  
  Review the files changed.

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [N/A]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [20230710].
  

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[jprestop]

I have reviewed the changes and verified that the new links work. All tests have passed. Thank you @hertneky for catching this and for making these changes! I approve this request.