Feature 313 consistent headers

[lisagoodrich]

Pull Request Testing

• Describe testing already performed for these changes:
  All of the chapters, sections and sub-sections are consistent across the different chapters. METcalcpy/docs/index.rst and METcalcpy/docs/Users_Guide/index.rst files have been updated to include ### for the title. Please note, there are no chapter sections in the index files. It will mess up the Table of Contents formatting in the left side menu window.

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  Please confirm all of the chapter, section and sub-section changes are accurate. Here is the feature branch web page: https://metcalcpy.readthedocs.io/en/feature_313_consistent_headers/Contributors_Guide/index.html

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

• Do these changes include sufficient testing updates? [Yes]

• 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 [7/21/23].
  

Pull Request Checklist

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[jprestop]

I have reviewed the changes and approve this request. Thank you for all of your work on this @lisagoodrich.