freebsd-status-report-process: Add article

Add a new article about the FreeBSD status report process created by
putting together content from

• website/content/en/status/_index.adoc;
• website/content/en/status/README (file is now removed);
• website/content/en/status/howto/_index.adoc (file is now removed).

Reviewed by: status (pauamma)
Approved by: doc (bcr)
Differential Revision: https://reviews.freebsd.org/D38919