Replace standards document with summary of standards-track PHEPs

[jtniehof]

#29, #33, #34, #35 propose replacing our standards document with standards-track PHEPs. On the PyHC telecon today (2024-09-23), @wtbarnes pointed out that it's nice our existing standards are a single document, easily digestible. @rebeccaringuette suggested some sort of summary document that builds on the standards PHEPs (which would be the definitive reference); @wtbarnes and @nabobalis concurred (that I noted).

Further discussion seemed to indicate a consensus that:

1. Such a document should be more than just gluing together the abstracts of relevant PHEPs and should have some level of individual crafting
2. But it should not be another heavy PHEP-like, approvals-required sort of document.

This would take the form of something like a summary paragraph describing the goals of the standards document, and potentially could be implemented by adding more detail on the PHEPs page, or as a separate document.

Ideas for format and process welcome.

[jtniehof]

My hope is we can find a process that makes sure this reflects community consensus without having to vote on every dang summary. It would be nice to have the implementation of a new summary be part of the discussion process for each standards-track PHEP (and if we want to require that, it could be added to a successor of PHEP1). And/or we can make revisiting the standards summary a regular activity of each PyHC meeting.

The good news is, right now we have no approved standards-track PHEPs, so we don't have to do much backfilling.

[rebeccaringuette]

Pretty sure someone else suggested this, but happy to support.
The idea was to have some sort of introductory paragraph, maybe two, then a bulleted list or table where the PHEP titles with their links are listed. PHEPs currently in proposal phase (please insert correct term here) would also be listed, but in grey as opposed to black.