Top level README is way out of date.

[jedwards4b]

Brief summary of bug

It refers to a spreadsheet that hasn't been updated since 2018 or so.

General bug information

CESM version you are using: [Output of git describe]

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Have you modified the code? (If so, please point us to you changes.): [Yes / No]

Details of bug

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Steps to reproduce the problem. Include externals description file(s) and link to public repository

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Screen output or log file showing the error message and context

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