Maintainer Handbook: Maintainer Entry Profile

As presented at the 2018 Linux Plumbers conference [1], the Maintainer
Entry Profile (formerly Subsystem Profile) is proposed as a way to reduce
friction between committers and maintainers and encourage conversations
amongst maintainers about common best practices. While coding-style,
submit-checklist, and submitting-drivers lay out some common expectations
there remain local customs and maintainer preferences that vary by
subsystem.

The profile contains documentation of some of the common policy
questions a contributor might have that are local to the subsystem /
device-driver, special considerations for the subsystem, or other
guidelines that are otherwise not covered by the top-level process
documents.

The initial and hopefully non-controversial headings in the profile are:

    Overview:
    General introduction to how the subsystem operates

    Submit Checklist Addendum:
    Mechanical items that gate submission staging, or other requirements
    that ...