Draft: WIP: reorganizing docs from perlmutter readiness page into perlmutter page tree

This MR is trying to organize content from https://docs.nersc.gov/performance/readiness into the perlmutter page tree into meaningful sections so its easy to find content. This was written before we got perlmutter and there was a disconnect in the location where this page was residing considering now most of the perlmutter specific pages are under System > Perlmutter

Shown below is an outline of page tree on left hand side. We have a grouping for Programming Models, Languages which sort of mimics the "Development" and "Developer Tools" page in the top-level.

If non-trivial please provide a summary of the changes here.

Submitters and reviewers please make sure

• internal links are relative and to the .md file
• avoid links named "here"
• alt-text for images is descriptive
• doesn't duplicate existing content
• spell check
• renders correctly
• does not include any identifiable information (real usernames, project names, etc)