Committers guide: wordsmith the section on maintainers

• remove an aside about reading the mailing list. This is taken care of by the later sentence about reading revision history
• use a slightly stronger admonition ("important" instead of "note") for the comments about not sending mail directly to the maintainer.
• Refer explicitly to the 'MAINTAINERS' file at the root of the tree
• Use the language of "asking for a review" instead of "sending the change to them" which, again, encourages a more public interaction.
• Remove the weasel language "it may help" and just encourage people to scan the history