help: mention -a and -g option, and 'git help <concept>' usage.
help: mention -a and -g option, and 'git help <concept>' usage.

Reword the overall help given at the end of "git help -a/-g" to
mention how to get help on individual commands and concepts.

Signed-off-by: Philip Oakley <a0e80625db756b4bd51d5507b8662a7e4f6837ad@iee.org>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git