process.rst: Perform minor cleanups

process.rst: Perform minor cleanups

- Use gender-neutral language to refer to the user, consistently.
- Reword a few places so that they read more naturally.
- Make the long standing practice around "Twilight Time" more clear,
  hopefully.
- Replace a reference to MAKEALL with a reference to CI testing as
  that's the current requirement.

Cc: Claudius Heine <ch@denx.de>
Cc: Martin Bonner <martingreybeard@gmail.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>