Feature 273 python requirements

[lisagoodrich]

Pull Request Testing

• Describe testing already performed for these changes:
  
  Added a literalinclude
  Added a Python Requirements section under "Requirements"
  Added This note, "The requirements below come directly from the requirements.txt file at the top level of the repository."

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  
  Please read the documentation carefully and make sure this is what we want.
  https://github.com/dtcenter/METdataio/blob/feature_273_python_requirements/docs/Users_Guide/installation.rst

I didn't remove this sentence, "METdataio also requires the Python packages pymysql, pandas, numpy, pyyaml, and lxml."
Please note, I couldn't find "pymysql" in the requirements.txt. Should this be removed?

• 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? [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 [2/15/24].
  

Pull Request Checklist

See the METplus Workflow for details.

• Add any new Python packages to the METplus Components Python Requirements table.
• Review the source issue metadata (required labels, projects, and milestone).
• Complete the PR definition above.
• Ensure the PR title matches the feature or bugfix branch name.
• Define the PR metadata, as permissions allow.
  Select: Reviewer(s)
  Select: Organization level software support Project or Repository level development cycle Project
  Select: Milestone as the version that will include these changes
• After submitting the PR, select the ⚙️ icon in the Development section of the right hand sidebar. Search for the issue that this PR will close and select it, if it is not already selected.
• After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
• Close the linked issue and delete your feature or bugfix branch from GitHub.

[jprestop]

Thanks for making these changes @lisagoodrich. I approve this request. I'll go ahead and squash and merge.