docs: update the development process document

Here's a set of changes updating Documentation/development-process.  I have
update kernel releases and relevant statistics, added information for a
couple of tools, zapped some trailing white space, and generally tried to
make it more closely match the current state of affairs.

[Typo fixes from Joe Perches and Nicolas Kaiser incorporated]

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Greg KH <greg@kroah.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>