Diag table documentation

[uramirez8707]

Description
This adds documentation for the diag_table.yaml

Fixes # (issue)

How Has This Been Tested?
documentation updates only

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes