Feature update 2603 mode.rst

[hertneky]

Update mode.rst to modify multivar_intensity to multivar_intensity_flag #2603

Expected Differences

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

Pull Request Testing

• Describe testing already performed for these changes:
  

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

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

• Do these changes include sufficient testing updates? [Yes or No]

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

• Please complete this pull request review by [Fill in date].
  

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[davidalbo]

Everything looks correct.